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ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU 

On a 144 thread system, `perf ftrace` takes about 20 seconds to start
up, due to calling synchronize_rcu() for each CPU.

  cat /proc/108560/stack
    0xc0003e7eb336f470
    __switch_to+0x2e0/0x480
    __wait_rcu_gp+0x20c/0x220
    synchronize_rcu+0x9c/0xc0
    ring_buffer_reset_cpu+0x88/0x2e0
    tracing_reset_online_cpus+0x84/0xe0
    tracing_open+0x1d4/0x1f0

On a system with 10x more threads, it starts to become an annoyance.

Batch these up so we disable all the per-cpu buffers first, then
synchronize_rcu() once, then reset each of the buffers. This brings
the time down to about 0.5s.

Link: https://lkml.kernel.org/r/20200625053403.2386972-1-npiggin@gmail.com

Tested-by: Anton Blanchard <anton@ozlabs.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
zero-sugar-mainline-defconfig
Nicholas Piggin 2020-06-25 15:34:03 +10:00 committed by Steven Rostedt (VMware)
parent 10464b4aa6
commit b23d7a5f4a
3 changed files with 77 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/ring_buffer.h
View File

@ -143,6 +143,7 @@ bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter);
unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu);
void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu);
void ring_buffer_reset_online_cpus(struct trace_buffer *buffer);
void ring_buffer_reset(struct trace_buffer *buffer);
#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP

93
kernel/trace/ring_buffer.c
View File

@ -270,6 +270,9 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
#define for_each_buffer_cpu(buffer, cpu) \
for_each_cpu(cpu, buffer->cpumask)
#define for_each_online_buffer_cpu(buffer, cpu) \
for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
#define TS_SHIFT 27
#define TS_MASK ((1ULL << TS_SHIFT) - 1)
#define TS_DELTA_TEST (~TS_MASK)
@ -4790,25 +4793,11 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
rb_head_page_activate(cpu_buffer);
}
/**
* ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
* @cpu: The CPU buffer to be reset
*/
void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
/* Must have disabled the cpu buffer then done a synchronize_rcu */
static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
unsigned long flags;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
atomic_inc(&cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
/* Make sure all commits have finished */
synchronize_rcu();
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
@ -4822,22 +4811,90 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
out:
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
/**
* ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
* @cpu: The CPU buffer to be reset
*/
void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
atomic_inc(&cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
/* Make sure all commits have finished */
synchronize_rcu();
reset_disabled_cpu_buffer(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
/**
* ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
* @cpu: The CPU buffer to be reset
*/
void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
for_each_online_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
}
/* Make sure all commits have finished */
synchronize_rcu();
for_each_online_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
reset_disabled_cpu_buffer(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
}
}
/**
* ring_buffer_reset - reset a ring buffer
* @buffer: The ring buffer to reset all cpu buffers
*/
void ring_buffer_reset(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
for_each_buffer_cpu(buffer, cpu)
ring_buffer_reset_cpu(buffer, cpu);
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
}
/* Make sure all commits have finished */
synchronize_rcu();
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
reset_disabled_cpu_buffer(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
}
}
EXPORT_SYMBOL_GPL(ring_buffer_reset);

4
kernel/trace/trace.c
View File

@ -2003,7 +2003,6 @@ static void tracing_reset_cpu(struct array_buffer *buf, int cpu)
void tracing_reset_online_cpus(struct array_buffer *buf)
{
struct trace_buffer *buffer = buf->buffer;
int cpu;
if (!buffer)
return;
@ -2015,8 +2014,7 @@ void tracing_reset_online_cpus(struct array_buffer *buf)
buf->time_start = buffer_ftrace_now(buf, buf->cpu);
for_each_online_cpu(cpu)
ring_buffer_reset_cpu(buffer, cpu);
ring_buffer_reset_online_cpus(buffer);
ring_buffer_record_enable(buffer);
}