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![Ingo Molnar](/assets/img/avatar_default.png)
Oprofile's ring-buffer use was not considered. Signed-off-by: Ingo Molnar <mingo@elte.hu>
468 lines
11 KiB
C
468 lines
11 KiB
C
/**
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* @file cpu_buffer.c
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*
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* @remark Copyright 2002-2009 OProfile authors
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* @remark Read the file COPYING
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*
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* @author John Levon <levon@movementarian.org>
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* @author Barry Kasindorf <barry.kasindorf@amd.com>
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* @author Robert Richter <robert.richter@amd.com>
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*
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* Each CPU has a local buffer that stores PC value/event
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* pairs. We also log context switches when we notice them.
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* Eventually each CPU's buffer is processed into the global
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* event buffer by sync_buffer().
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*
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* We use a local buffer for two reasons: an NMI or similar
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* interrupt cannot synchronise, and high sampling rates
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* would lead to catastrophic global synchronisation if
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* a global buffer was used.
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*/
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#include <linux/sched.h>
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#include <linux/oprofile.h>
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#include <linux/vmalloc.h>
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#include <linux/errno.h>
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#include "event_buffer.h"
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#include "cpu_buffer.h"
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#include "buffer_sync.h"
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#include "oprof.h"
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#define OP_BUFFER_FLAGS 0
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/*
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* Read and write access is using spin locking. Thus, writing to the
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* buffer by NMI handler (x86) could occur also during critical
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* sections when reading the buffer. To avoid this, there are 2
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* buffers for independent read and write access. Read access is in
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* process context only, write access only in the NMI handler. If the
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* read buffer runs empty, both buffers are swapped atomically. There
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* is potentially a small window during swapping where the buffers are
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* disabled and samples could be lost.
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*
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* Using 2 buffers is a little bit overhead, but the solution is clear
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* and does not require changes in the ring buffer implementation. It
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* can be changed to a single buffer solution when the ring buffer
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* access is implemented as non-locking atomic code.
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*/
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static struct ring_buffer *op_ring_buffer_read;
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static struct ring_buffer *op_ring_buffer_write;
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DEFINE_PER_CPU(struct oprofile_cpu_buffer, cpu_buffer);
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static void wq_sync_buffer(struct work_struct *work);
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#define DEFAULT_TIMER_EXPIRE (HZ / 10)
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static int work_enabled;
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unsigned long oprofile_get_cpu_buffer_size(void)
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{
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return oprofile_cpu_buffer_size;
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}
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void oprofile_cpu_buffer_inc_smpl_lost(void)
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{
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struct oprofile_cpu_buffer *cpu_buf
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= &__get_cpu_var(cpu_buffer);
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cpu_buf->sample_lost_overflow++;
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}
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void free_cpu_buffers(void)
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{
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if (op_ring_buffer_read)
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ring_buffer_free(op_ring_buffer_read);
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op_ring_buffer_read = NULL;
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if (op_ring_buffer_write)
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ring_buffer_free(op_ring_buffer_write);
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op_ring_buffer_write = NULL;
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}
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int alloc_cpu_buffers(void)
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{
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int i;
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unsigned long buffer_size = oprofile_cpu_buffer_size;
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op_ring_buffer_read = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
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if (!op_ring_buffer_read)
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goto fail;
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op_ring_buffer_write = ring_buffer_alloc(buffer_size, OP_BUFFER_FLAGS);
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if (!op_ring_buffer_write)
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goto fail;
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for_each_possible_cpu(i) {
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struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
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b->last_task = NULL;
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b->last_is_kernel = -1;
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b->tracing = 0;
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b->buffer_size = buffer_size;
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b->sample_received = 0;
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b->sample_lost_overflow = 0;
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b->backtrace_aborted = 0;
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b->sample_invalid_eip = 0;
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b->cpu = i;
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INIT_DELAYED_WORK(&b->work, wq_sync_buffer);
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}
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return 0;
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fail:
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free_cpu_buffers();
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return -ENOMEM;
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}
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void start_cpu_work(void)
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{
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int i;
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work_enabled = 1;
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for_each_online_cpu(i) {
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struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
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/*
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* Spread the work by 1 jiffy per cpu so they dont all
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* fire at once.
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*/
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schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
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}
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}
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void end_cpu_work(void)
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{
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int i;
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work_enabled = 0;
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for_each_online_cpu(i) {
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struct oprofile_cpu_buffer *b = &per_cpu(cpu_buffer, i);
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cancel_delayed_work(&b->work);
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}
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flush_scheduled_work();
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}
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/*
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* This function prepares the cpu buffer to write a sample.
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*
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* Struct op_entry is used during operations on the ring buffer while
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* struct op_sample contains the data that is stored in the ring
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* buffer. Struct entry can be uninitialized. The function reserves a
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* data array that is specified by size. Use
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* op_cpu_buffer_write_commit() after preparing the sample. In case of
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* errors a null pointer is returned, otherwise the pointer to the
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* sample.
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*
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*/
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struct op_sample
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*op_cpu_buffer_write_reserve(struct op_entry *entry, unsigned long size)
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{
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entry->event = ring_buffer_lock_reserve
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(op_ring_buffer_write, sizeof(struct op_sample) +
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size * sizeof(entry->sample->data[0]));
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if (entry->event)
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entry->sample = ring_buffer_event_data(entry->event);
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else
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entry->sample = NULL;
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if (!entry->sample)
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return NULL;
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entry->size = size;
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entry->data = entry->sample->data;
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return entry->sample;
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}
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int op_cpu_buffer_write_commit(struct op_entry *entry)
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{
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return ring_buffer_unlock_commit(op_ring_buffer_write, entry->event);
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}
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struct op_sample *op_cpu_buffer_read_entry(struct op_entry *entry, int cpu)
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{
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struct ring_buffer_event *e;
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e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
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if (e)
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goto event;
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if (ring_buffer_swap_cpu(op_ring_buffer_read,
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op_ring_buffer_write,
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cpu))
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return NULL;
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e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL);
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if (e)
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goto event;
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return NULL;
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event:
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entry->event = e;
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entry->sample = ring_buffer_event_data(e);
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entry->size = (ring_buffer_event_length(e) - sizeof(struct op_sample))
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/ sizeof(entry->sample->data[0]);
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entry->data = entry->sample->data;
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return entry->sample;
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}
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unsigned long op_cpu_buffer_entries(int cpu)
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{
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return ring_buffer_entries_cpu(op_ring_buffer_read, cpu)
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+ ring_buffer_entries_cpu(op_ring_buffer_write, cpu);
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}
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static int
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op_add_code(struct oprofile_cpu_buffer *cpu_buf, unsigned long backtrace,
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int is_kernel, struct task_struct *task)
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{
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struct op_entry entry;
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struct op_sample *sample;
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unsigned long flags;
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int size;
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flags = 0;
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if (backtrace)
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flags |= TRACE_BEGIN;
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/* notice a switch from user->kernel or vice versa */
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is_kernel = !!is_kernel;
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if (cpu_buf->last_is_kernel != is_kernel) {
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cpu_buf->last_is_kernel = is_kernel;
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flags |= KERNEL_CTX_SWITCH;
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if (is_kernel)
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flags |= IS_KERNEL;
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}
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/* notice a task switch */
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if (cpu_buf->last_task != task) {
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cpu_buf->last_task = task;
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flags |= USER_CTX_SWITCH;
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}
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if (!flags)
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/* nothing to do */
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return 0;
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if (flags & USER_CTX_SWITCH)
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size = 1;
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else
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size = 0;
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sample = op_cpu_buffer_write_reserve(&entry, size);
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if (!sample)
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return -ENOMEM;
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sample->eip = ESCAPE_CODE;
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sample->event = flags;
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if (size)
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op_cpu_buffer_add_data(&entry, (unsigned long)task);
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op_cpu_buffer_write_commit(&entry);
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return 0;
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}
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static inline int
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op_add_sample(struct oprofile_cpu_buffer *cpu_buf,
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unsigned long pc, unsigned long event)
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{
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struct op_entry entry;
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struct op_sample *sample;
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sample = op_cpu_buffer_write_reserve(&entry, 0);
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if (!sample)
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return -ENOMEM;
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sample->eip = pc;
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sample->event = event;
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return op_cpu_buffer_write_commit(&entry);
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}
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/*
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* This must be safe from any context.
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*
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* is_kernel is needed because on some architectures you cannot
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* tell if you are in kernel or user space simply by looking at
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* pc. We tag this in the buffer by generating kernel enter/exit
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* events whenever is_kernel changes
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*/
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static int
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log_sample(struct oprofile_cpu_buffer *cpu_buf, unsigned long pc,
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unsigned long backtrace, int is_kernel, unsigned long event)
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{
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cpu_buf->sample_received++;
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if (pc == ESCAPE_CODE) {
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cpu_buf->sample_invalid_eip++;
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return 0;
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}
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if (op_add_code(cpu_buf, backtrace, is_kernel, current))
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goto fail;
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if (op_add_sample(cpu_buf, pc, event))
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goto fail;
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return 1;
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fail:
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cpu_buf->sample_lost_overflow++;
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return 0;
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}
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static inline void oprofile_begin_trace(struct oprofile_cpu_buffer *cpu_buf)
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{
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cpu_buf->tracing = 1;
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}
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static inline void oprofile_end_trace(struct oprofile_cpu_buffer *cpu_buf)
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{
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cpu_buf->tracing = 0;
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}
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static inline void
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__oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
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unsigned long event, int is_kernel)
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{
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struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
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unsigned long backtrace = oprofile_backtrace_depth;
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/*
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* if log_sample() fail we can't backtrace since we lost the
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* source of this event
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*/
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if (!log_sample(cpu_buf, pc, backtrace, is_kernel, event))
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/* failed */
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return;
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if (!backtrace)
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return;
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oprofile_begin_trace(cpu_buf);
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oprofile_ops.backtrace(regs, backtrace);
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oprofile_end_trace(cpu_buf);
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}
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void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
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unsigned long event, int is_kernel)
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{
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__oprofile_add_ext_sample(pc, regs, event, is_kernel);
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}
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void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
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{
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int is_kernel = !user_mode(regs);
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unsigned long pc = profile_pc(regs);
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__oprofile_add_ext_sample(pc, regs, event, is_kernel);
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}
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/*
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* Add samples with data to the ring buffer.
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*
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* Use oprofile_add_data(&entry, val) to add data and
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* oprofile_write_commit(&entry) to commit the sample.
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*/
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void
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oprofile_write_reserve(struct op_entry *entry, struct pt_regs * const regs,
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unsigned long pc, int code, int size)
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{
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struct op_sample *sample;
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int is_kernel = !user_mode(regs);
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struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
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cpu_buf->sample_received++;
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/* no backtraces for samples with data */
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if (op_add_code(cpu_buf, 0, is_kernel, current))
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goto fail;
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sample = op_cpu_buffer_write_reserve(entry, size + 2);
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if (!sample)
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goto fail;
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sample->eip = ESCAPE_CODE;
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sample->event = 0; /* no flags */
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op_cpu_buffer_add_data(entry, code);
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op_cpu_buffer_add_data(entry, pc);
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return;
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fail:
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entry->event = NULL;
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cpu_buf->sample_lost_overflow++;
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}
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int oprofile_add_data(struct op_entry *entry, unsigned long val)
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{
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if (!entry->event)
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return 0;
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return op_cpu_buffer_add_data(entry, val);
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}
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int oprofile_write_commit(struct op_entry *entry)
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{
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if (!entry->event)
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return -EINVAL;
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return op_cpu_buffer_write_commit(entry);
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}
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void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
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{
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struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
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log_sample(cpu_buf, pc, 0, is_kernel, event);
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}
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void oprofile_add_trace(unsigned long pc)
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{
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struct oprofile_cpu_buffer *cpu_buf = &__get_cpu_var(cpu_buffer);
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if (!cpu_buf->tracing)
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return;
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/*
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* broken frame can give an eip with the same value as an
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* escape code, abort the trace if we get it
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*/
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if (pc == ESCAPE_CODE)
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goto fail;
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if (op_add_sample(cpu_buf, pc, 0))
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goto fail;
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return;
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fail:
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cpu_buf->tracing = 0;
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cpu_buf->backtrace_aborted++;
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return;
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}
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/*
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* This serves to avoid cpu buffer overflow, and makes sure
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* the task mortuary progresses
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*
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* By using schedule_delayed_work_on and then schedule_delayed_work
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* we guarantee this will stay on the correct cpu
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*/
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static void wq_sync_buffer(struct work_struct *work)
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{
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struct oprofile_cpu_buffer *b =
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container_of(work, struct oprofile_cpu_buffer, work.work);
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if (b->cpu != smp_processor_id()) {
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printk(KERN_DEBUG "WQ on CPU%d, prefer CPU%d\n",
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smp_processor_id(), b->cpu);
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if (!cpu_online(b->cpu)) {
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cancel_delayed_work(&b->work);
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return;
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}
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}
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sync_buffer(b->cpu);
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/* don't re-add the work if we're shutting down */
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if (work_enabled)
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schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
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}
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