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

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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>
This commit is contained in:
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
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include/linux/ring_buffer.h
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@@ -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