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![David Miller](/assets/img/avatar_default.png)
When performing a non-consuming read, a synchronize_sched() is performed once for every cpu which is actively tracing. This is very expensive, and can make it take several seconds to open up the 'trace' file with lots of cpus. Only one synchronize_sched() call is actually necessary. What is desired is for all cpus to see the disabling state change. So we transform the existing sequence: for_each_cpu() { ring_buffer_read_start(); } where each ring_buffer_start() call performs a synchronize_sched(), into the following: for_each_cpu() { ring_buffer_read_prepare(); } ring_buffer_read_prepare_sync(); for_each_cpu() { ring_buffer_read_start(); } wherein only the single ring_buffer_read_prepare_sync() call needs to do the synchronize_sched(). The first phase, via ring_buffer_read_prepare(), allocates the 'iter' memory and increments ->record_disabled. In the second phase, ring_buffer_read_prepare_sync() makes sure this ->record_disabled state is visible fully to all cpus. And in the final third phase, the ring_buffer_read_start() calls reset the 'iter' objects allocated in the first phase since we now know that none of the cpus are adding trace entries any more. This makes openning the 'trace' file nearly instantaneous on a sparc64 Niagara2 box with 128 cpus tracing. Signed-off-by: David S. Miller <davem@davemloft.net> LKML-Reference: <20100420.154711.11246950.davem@davemloft.net> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
196 lines
6.1 KiB
C
196 lines
6.1 KiB
C
#ifndef _LINUX_RING_BUFFER_H
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#define _LINUX_RING_BUFFER_H
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#include <linux/kmemcheck.h>
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#include <linux/mm.h>
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#include <linux/seq_file.h>
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struct ring_buffer;
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struct ring_buffer_iter;
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/*
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* Don't refer to this struct directly, use functions below.
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*/
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struct ring_buffer_event {
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kmemcheck_bitfield_begin(bitfield);
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u32 type_len:5, time_delta:27;
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kmemcheck_bitfield_end(bitfield);
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u32 array[];
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};
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/**
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* enum ring_buffer_type - internal ring buffer types
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*
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* @RINGBUF_TYPE_PADDING: Left over page padding or discarded event
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* If time_delta is 0:
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* array is ignored
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* size is variable depending on how much
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* padding is needed
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* If time_delta is non zero:
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* array[0] holds the actual length
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* size = 4 + length (bytes)
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*
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* @RINGBUF_TYPE_TIME_EXTEND: Extend the time delta
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* array[0] = time delta (28 .. 59)
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* size = 8 bytes
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*
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* @RINGBUF_TYPE_TIME_STAMP: Sync time stamp with external clock
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* array[0] = tv_nsec
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* array[1..2] = tv_sec
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* size = 16 bytes
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*
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* <= @RINGBUF_TYPE_DATA_TYPE_LEN_MAX:
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* Data record
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* If type_len is zero:
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* array[0] holds the actual length
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* array[1..(length+3)/4] holds data
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* size = 4 + length (bytes)
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* else
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* length = type_len << 2
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* array[0..(length+3)/4-1] holds data
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* size = 4 + length (bytes)
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*/
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enum ring_buffer_type {
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RINGBUF_TYPE_DATA_TYPE_LEN_MAX = 28,
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RINGBUF_TYPE_PADDING,
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RINGBUF_TYPE_TIME_EXTEND,
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/* FIXME: RINGBUF_TYPE_TIME_STAMP not implemented */
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RINGBUF_TYPE_TIME_STAMP,
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};
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unsigned ring_buffer_event_length(struct ring_buffer_event *event);
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void *ring_buffer_event_data(struct ring_buffer_event *event);
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/**
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* ring_buffer_event_time_delta - return the delta timestamp of the event
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* @event: the event to get the delta timestamp of
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*
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* The delta timestamp is the 27 bit timestamp since the last event.
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*/
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static inline unsigned
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ring_buffer_event_time_delta(struct ring_buffer_event *event)
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{
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return event->time_delta;
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}
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/*
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* ring_buffer_discard_commit will remove an event that has not
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* ben committed yet. If this is used, then ring_buffer_unlock_commit
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* must not be called on the discarded event. This function
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* will try to remove the event from the ring buffer completely
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* if another event has not been written after it.
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*
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* Example use:
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*
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* if (some_condition)
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* ring_buffer_discard_commit(buffer, event);
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* else
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* ring_buffer_unlock_commit(buffer, event);
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*/
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void ring_buffer_discard_commit(struct ring_buffer *buffer,
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struct ring_buffer_event *event);
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/*
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* size is in bytes for each per CPU buffer.
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*/
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struct ring_buffer *
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__ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *key);
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/*
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* Because the ring buffer is generic, if other users of the ring buffer get
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* traced by ftrace, it can produce lockdep warnings. We need to keep each
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* ring buffer's lock class separate.
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*/
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#define ring_buffer_alloc(size, flags) \
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({ \
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static struct lock_class_key __key; \
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__ring_buffer_alloc((size), (flags), &__key); \
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})
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void ring_buffer_free(struct ring_buffer *buffer);
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int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size);
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struct ring_buffer_event *ring_buffer_lock_reserve(struct ring_buffer *buffer,
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unsigned long length);
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int ring_buffer_unlock_commit(struct ring_buffer *buffer,
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struct ring_buffer_event *event);
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int ring_buffer_write(struct ring_buffer *buffer,
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unsigned long length, void *data);
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struct ring_buffer_event *
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ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
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unsigned long *lost_events);
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struct ring_buffer_event *
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ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
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unsigned long *lost_events);
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struct ring_buffer_iter *
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ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu);
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void ring_buffer_read_prepare_sync(void);
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void ring_buffer_read_start(struct ring_buffer_iter *iter);
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void ring_buffer_read_finish(struct ring_buffer_iter *iter);
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struct ring_buffer_event *
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ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts);
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struct ring_buffer_event *
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ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts);
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void ring_buffer_iter_reset(struct ring_buffer_iter *iter);
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int ring_buffer_iter_empty(struct ring_buffer_iter *iter);
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unsigned long ring_buffer_size(struct ring_buffer *buffer);
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void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu);
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void ring_buffer_reset(struct ring_buffer *buffer);
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#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
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int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
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struct ring_buffer *buffer_b, int cpu);
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#else
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static inline int
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ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
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struct ring_buffer *buffer_b, int cpu)
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{
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return -ENODEV;
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}
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#endif
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int ring_buffer_empty(struct ring_buffer *buffer);
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int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu);
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void ring_buffer_record_disable(struct ring_buffer *buffer);
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void ring_buffer_record_enable(struct ring_buffer *buffer);
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void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu);
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void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_entries(struct ring_buffer *buffer);
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unsigned long ring_buffer_overruns(struct ring_buffer *buffer);
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unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu);
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u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu);
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void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
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int cpu, u64 *ts);
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void ring_buffer_set_clock(struct ring_buffer *buffer,
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u64 (*clock)(void));
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size_t ring_buffer_page_len(void *page);
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void *ring_buffer_alloc_read_page(struct ring_buffer *buffer);
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void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data);
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int ring_buffer_read_page(struct ring_buffer *buffer, void **data_page,
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size_t len, int cpu, int full);
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struct trace_seq;
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int ring_buffer_print_entry_header(struct trace_seq *s);
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int ring_buffer_print_page_header(struct trace_seq *s);
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enum ring_buffer_flags {
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RB_FL_OVERWRITE = 1 << 0,
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};
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#endif /* _LINUX_RING_BUFFER_H */
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