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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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![Ming Lei](/assets/img/avatar_default.png)
When the allocation process is scheduled back and the mapped hw queue is changed, fake one extra wake up on previous queue for compensating wake up miss, so other allocations on the previous queue won't be starved. This patch fixes one request allocation hang issue, which can be triggered easily in case of very low nr_request. The race is as follows: 1) 2 hw queues, nr_requests are 2, and wake_batch is one 2) there are 3 waiters on hw queue 0 3) two in-flight requests in hw queue 0 are completed, and only two waiters of 3 are waken up because of wake_batch, but both the two waiters can be scheduled to another CPU and cause to switch to hw queue 1 4) then the 3rd waiter will wait for ever, since no in-flight request is in hw queue 0 any more. 5) this patch fixes it by the fake wakeup when waiter is scheduled to another hw queue Cc: <stable@vger.kernel.org> Reviewed-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> Modified commit message to make it clearer, and make it apply on top of the 4.18 branch. Signed-off-by: Jens Axboe <axboe@kernel.dk>
581 lines
14 KiB
C
581 lines
14 KiB
C
/*
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* Copyright (C) 2016 Facebook
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* Copyright (C) 2013-2014 Jens Axboe
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#include <linux/sched.h>
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#include <linux/random.h>
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#include <linux/sbitmap.h>
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#include <linux/seq_file.h>
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int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
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gfp_t flags, int node)
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{
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unsigned int bits_per_word;
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unsigned int i;
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if (shift < 0) {
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shift = ilog2(BITS_PER_LONG);
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/*
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* If the bitmap is small, shrink the number of bits per word so
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* we spread over a few cachelines, at least. If less than 4
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* bits, just forget about it, it's not going to work optimally
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* anyway.
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*/
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if (depth >= 4) {
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while ((4U << shift) > depth)
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shift--;
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}
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}
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bits_per_word = 1U << shift;
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if (bits_per_word > BITS_PER_LONG)
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return -EINVAL;
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sb->shift = shift;
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sb->depth = depth;
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sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
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if (depth == 0) {
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sb->map = NULL;
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return 0;
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}
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sb->map = kzalloc_node(sb->map_nr * sizeof(*sb->map), flags, node);
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if (!sb->map)
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return -ENOMEM;
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for (i = 0; i < sb->map_nr; i++) {
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sb->map[i].depth = min(depth, bits_per_word);
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depth -= sb->map[i].depth;
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}
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return 0;
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}
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EXPORT_SYMBOL_GPL(sbitmap_init_node);
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void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
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{
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unsigned int bits_per_word = 1U << sb->shift;
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unsigned int i;
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sb->depth = depth;
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sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
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for (i = 0; i < sb->map_nr; i++) {
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sb->map[i].depth = min(depth, bits_per_word);
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depth -= sb->map[i].depth;
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}
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}
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EXPORT_SYMBOL_GPL(sbitmap_resize);
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static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
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unsigned int hint, bool wrap)
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{
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unsigned int orig_hint = hint;
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int nr;
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while (1) {
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nr = find_next_zero_bit(word, depth, hint);
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if (unlikely(nr >= depth)) {
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/*
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* We started with an offset, and we didn't reset the
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* offset to 0 in a failure case, so start from 0 to
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* exhaust the map.
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*/
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if (orig_hint && hint && wrap) {
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hint = orig_hint = 0;
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continue;
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}
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return -1;
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}
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if (!test_and_set_bit_lock(nr, word))
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break;
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hint = nr + 1;
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if (hint >= depth - 1)
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hint = 0;
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}
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return nr;
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}
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int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
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{
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unsigned int i, index;
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int nr = -1;
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index = SB_NR_TO_INDEX(sb, alloc_hint);
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for (i = 0; i < sb->map_nr; i++) {
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nr = __sbitmap_get_word(&sb->map[index].word,
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sb->map[index].depth,
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SB_NR_TO_BIT(sb, alloc_hint),
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!round_robin);
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if (nr != -1) {
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nr += index << sb->shift;
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break;
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}
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/* Jump to next index. */
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index++;
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alloc_hint = index << sb->shift;
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if (index >= sb->map_nr) {
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index = 0;
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alloc_hint = 0;
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}
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}
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return nr;
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}
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EXPORT_SYMBOL_GPL(sbitmap_get);
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int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
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unsigned long shallow_depth)
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{
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unsigned int i, index;
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int nr = -1;
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index = SB_NR_TO_INDEX(sb, alloc_hint);
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for (i = 0; i < sb->map_nr; i++) {
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nr = __sbitmap_get_word(&sb->map[index].word,
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min(sb->map[index].depth, shallow_depth),
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SB_NR_TO_BIT(sb, alloc_hint), true);
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if (nr != -1) {
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nr += index << sb->shift;
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break;
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}
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/* Jump to next index. */
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index++;
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alloc_hint = index << sb->shift;
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if (index >= sb->map_nr) {
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index = 0;
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alloc_hint = 0;
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}
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}
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return nr;
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}
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EXPORT_SYMBOL_GPL(sbitmap_get_shallow);
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bool sbitmap_any_bit_set(const struct sbitmap *sb)
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{
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unsigned int i;
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for (i = 0; i < sb->map_nr; i++) {
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if (sb->map[i].word)
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return true;
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}
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return false;
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}
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EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
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bool sbitmap_any_bit_clear(const struct sbitmap *sb)
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{
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unsigned int i;
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for (i = 0; i < sb->map_nr; i++) {
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const struct sbitmap_word *word = &sb->map[i];
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unsigned long ret;
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ret = find_first_zero_bit(&word->word, word->depth);
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if (ret < word->depth)
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return true;
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}
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return false;
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}
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EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
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unsigned int sbitmap_weight(const struct sbitmap *sb)
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{
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unsigned int i, weight = 0;
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for (i = 0; i < sb->map_nr; i++) {
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const struct sbitmap_word *word = &sb->map[i];
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weight += bitmap_weight(&word->word, word->depth);
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}
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return weight;
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}
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EXPORT_SYMBOL_GPL(sbitmap_weight);
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void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
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{
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seq_printf(m, "depth=%u\n", sb->depth);
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seq_printf(m, "busy=%u\n", sbitmap_weight(sb));
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seq_printf(m, "bits_per_word=%u\n", 1U << sb->shift);
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seq_printf(m, "map_nr=%u\n", sb->map_nr);
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}
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EXPORT_SYMBOL_GPL(sbitmap_show);
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static inline void emit_byte(struct seq_file *m, unsigned int offset, u8 byte)
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{
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if ((offset & 0xf) == 0) {
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if (offset != 0)
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seq_putc(m, '\n');
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seq_printf(m, "%08x:", offset);
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}
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if ((offset & 0x1) == 0)
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seq_putc(m, ' ');
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seq_printf(m, "%02x", byte);
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}
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void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
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{
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u8 byte = 0;
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unsigned int byte_bits = 0;
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unsigned int offset = 0;
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int i;
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for (i = 0; i < sb->map_nr; i++) {
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unsigned long word = READ_ONCE(sb->map[i].word);
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unsigned int word_bits = READ_ONCE(sb->map[i].depth);
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while (word_bits > 0) {
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unsigned int bits = min(8 - byte_bits, word_bits);
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byte |= (word & (BIT(bits) - 1)) << byte_bits;
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byte_bits += bits;
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if (byte_bits == 8) {
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emit_byte(m, offset, byte);
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byte = 0;
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byte_bits = 0;
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offset++;
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}
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word >>= bits;
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word_bits -= bits;
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}
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}
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if (byte_bits) {
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emit_byte(m, offset, byte);
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offset++;
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}
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if (offset)
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seq_putc(m, '\n');
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}
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EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);
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static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq,
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unsigned int depth)
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{
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unsigned int wake_batch;
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unsigned int shallow_depth;
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/*
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* For each batch, we wake up one queue. We need to make sure that our
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* batch size is small enough that the full depth of the bitmap,
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* potentially limited by a shallow depth, is enough to wake up all of
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* the queues.
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*
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* Each full word of the bitmap has bits_per_word bits, and there might
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* be a partial word. There are depth / bits_per_word full words and
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* depth % bits_per_word bits left over. In bitwise arithmetic:
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*
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* bits_per_word = 1 << shift
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* depth / bits_per_word = depth >> shift
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* depth % bits_per_word = depth & ((1 << shift) - 1)
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*
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* Each word can be limited to sbq->min_shallow_depth bits.
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*/
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shallow_depth = min(1U << sbq->sb.shift, sbq->min_shallow_depth);
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depth = ((depth >> sbq->sb.shift) * shallow_depth +
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min(depth & ((1U << sbq->sb.shift) - 1), shallow_depth));
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wake_batch = clamp_t(unsigned int, depth / SBQ_WAIT_QUEUES, 1,
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SBQ_WAKE_BATCH);
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return wake_batch;
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}
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int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
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int shift, bool round_robin, gfp_t flags, int node)
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{
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int ret;
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int i;
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ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
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if (ret)
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return ret;
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sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
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if (!sbq->alloc_hint) {
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sbitmap_free(&sbq->sb);
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return -ENOMEM;
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}
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if (depth && !round_robin) {
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for_each_possible_cpu(i)
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*per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
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}
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sbq->min_shallow_depth = UINT_MAX;
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sbq->wake_batch = sbq_calc_wake_batch(sbq, depth);
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atomic_set(&sbq->wake_index, 0);
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sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
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if (!sbq->ws) {
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free_percpu(sbq->alloc_hint);
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sbitmap_free(&sbq->sb);
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return -ENOMEM;
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}
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for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
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init_waitqueue_head(&sbq->ws[i].wait);
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atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
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}
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sbq->round_robin = round_robin;
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return 0;
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}
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EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
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static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
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unsigned int depth)
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{
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unsigned int wake_batch = sbq_calc_wake_batch(sbq, depth);
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int i;
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if (sbq->wake_batch != wake_batch) {
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WRITE_ONCE(sbq->wake_batch, wake_batch);
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/*
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* Pairs with the memory barrier in sbitmap_queue_wake_up()
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* to ensure that the batch size is updated before the wait
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* counts.
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*/
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smp_mb__before_atomic();
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for (i = 0; i < SBQ_WAIT_QUEUES; i++)
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atomic_set(&sbq->ws[i].wait_cnt, 1);
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}
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}
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void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
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{
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sbitmap_queue_update_wake_batch(sbq, depth);
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sbitmap_resize(&sbq->sb, depth);
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}
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EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
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int __sbitmap_queue_get(struct sbitmap_queue *sbq)
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{
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unsigned int hint, depth;
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int nr;
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hint = this_cpu_read(*sbq->alloc_hint);
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depth = READ_ONCE(sbq->sb.depth);
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if (unlikely(hint >= depth)) {
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hint = depth ? prandom_u32() % depth : 0;
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this_cpu_write(*sbq->alloc_hint, hint);
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}
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nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
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if (nr == -1) {
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/* If the map is full, a hint won't do us much good. */
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this_cpu_write(*sbq->alloc_hint, 0);
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} else if (nr == hint || unlikely(sbq->round_robin)) {
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/* Only update the hint if we used it. */
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hint = nr + 1;
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if (hint >= depth - 1)
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hint = 0;
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this_cpu_write(*sbq->alloc_hint, hint);
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}
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return nr;
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}
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EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
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int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
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unsigned int shallow_depth)
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{
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unsigned int hint, depth;
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int nr;
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WARN_ON_ONCE(shallow_depth < sbq->min_shallow_depth);
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hint = this_cpu_read(*sbq->alloc_hint);
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depth = READ_ONCE(sbq->sb.depth);
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if (unlikely(hint >= depth)) {
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hint = depth ? prandom_u32() % depth : 0;
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this_cpu_write(*sbq->alloc_hint, hint);
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}
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nr = sbitmap_get_shallow(&sbq->sb, hint, shallow_depth);
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if (nr == -1) {
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/* If the map is full, a hint won't do us much good. */
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this_cpu_write(*sbq->alloc_hint, 0);
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} else if (nr == hint || unlikely(sbq->round_robin)) {
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/* Only update the hint if we used it. */
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hint = nr + 1;
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if (hint >= depth - 1)
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hint = 0;
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this_cpu_write(*sbq->alloc_hint, hint);
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}
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return nr;
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}
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EXPORT_SYMBOL_GPL(__sbitmap_queue_get_shallow);
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void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq,
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unsigned int min_shallow_depth)
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{
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sbq->min_shallow_depth = min_shallow_depth;
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sbitmap_queue_update_wake_batch(sbq, sbq->sb.depth);
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}
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EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);
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static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
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{
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int i, wake_index;
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wake_index = atomic_read(&sbq->wake_index);
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for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
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struct sbq_wait_state *ws = &sbq->ws[wake_index];
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if (waitqueue_active(&ws->wait)) {
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int o = atomic_read(&sbq->wake_index);
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if (wake_index != o)
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atomic_cmpxchg(&sbq->wake_index, o, wake_index);
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return ws;
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}
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wake_index = sbq_index_inc(wake_index);
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}
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return NULL;
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}
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static bool __sbq_wake_up(struct sbitmap_queue *sbq)
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{
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struct sbq_wait_state *ws;
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unsigned int wake_batch;
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int wait_cnt;
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ws = sbq_wake_ptr(sbq);
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if (!ws)
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return false;
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wait_cnt = atomic_dec_return(&ws->wait_cnt);
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if (wait_cnt <= 0) {
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int ret;
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wake_batch = READ_ONCE(sbq->wake_batch);
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/*
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* Pairs with the memory barrier in sbitmap_queue_resize() to
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* ensure that we see the batch size update before the wait
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* count is reset.
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*/
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smp_mb__before_atomic();
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/*
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* For concurrent callers of this, the one that failed the
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* atomic_cmpxhcg() race should call this function again
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* to wakeup a new batch on a different 'ws'.
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*/
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ret = atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch);
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if (ret == wait_cnt) {
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sbq_index_atomic_inc(&sbq->wake_index);
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wake_up_nr(&ws->wait, wake_batch);
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return false;
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}
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return true;
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}
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return false;
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}
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void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
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{
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while (__sbq_wake_up(sbq))
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;
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}
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EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
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void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
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unsigned int cpu)
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{
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sbitmap_clear_bit_unlock(&sbq->sb, nr);
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/*
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|
* Pairs with the memory barrier in set_current_state() to ensure the
|
|
* proper ordering of clear_bit_unlock()/waitqueue_active() in the waker
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* and test_and_set_bit_lock()/prepare_to_wait()/finish_wait() in the
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* waiter. See the comment on waitqueue_active().
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*/
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smp_mb__after_atomic();
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sbitmap_queue_wake_up(sbq);
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|
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if (likely(!sbq->round_robin && nr < sbq->sb.depth))
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*per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
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}
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EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
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|
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void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
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|
{
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|
int i, wake_index;
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|
|
|
/*
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|
* Pairs with the memory barrier in set_current_state() like in
|
|
* sbitmap_queue_wake_up().
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|
*/
|
|
smp_mb();
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|
wake_index = atomic_read(&sbq->wake_index);
|
|
for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
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|
struct sbq_wait_state *ws = &sbq->ws[wake_index];
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|
|
|
if (waitqueue_active(&ws->wait))
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|
wake_up(&ws->wait);
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|
|
|
wake_index = sbq_index_inc(wake_index);
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|
}
|
|
}
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|
EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);
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|
|
|
void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
|
|
{
|
|
bool first;
|
|
int i;
|
|
|
|
sbitmap_show(&sbq->sb, m);
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|
|
|
seq_puts(m, "alloc_hint={");
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|
first = true;
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|
for_each_possible_cpu(i) {
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|
if (!first)
|
|
seq_puts(m, ", ");
|
|
first = false;
|
|
seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
|
|
}
|
|
seq_puts(m, "}\n");
|
|
|
|
seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
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|
seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
|
|
|
|
seq_puts(m, "ws={\n");
|
|
for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
|
|
struct sbq_wait_state *ws = &sbq->ws[i];
|
|
|
|
seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
|
|
atomic_read(&ws->wait_cnt),
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|
waitqueue_active(&ws->wait) ? "active" : "inactive");
|
|
}
|
|
seq_puts(m, "}\n");
|
|
|
|
seq_printf(m, "round_robin=%d\n", sbq->round_robin);
|
|
seq_printf(m, "min_shallow_depth=%u\n", sbq->min_shallow_depth);
|
|
}
|
|
EXPORT_SYMBOL_GPL(sbitmap_queue_show);
|