linux-kernel - Re: [PATCH] perf/core: Add a tracepoint for perf sampling

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Date:	Fri, 29 Jul 2016 16:21:00 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Brendan Gregg <bgregg@...flix.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
	Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH] perf/core: Add a tracepoint for perf sampling

Em Tue, Jul 19, 2016 at 11:20:48PM +0000, Brendan Gregg escreveu:
> When perf is performing hrtimer-based sampling, this tracepoint can be used
> by BPF to run additional logic on each sample. For example, BPF can fetch
> stack traces and frequency count them in kernel context, for an efficient
> profiler.

Could you provide a complete experience? I.e. together with this patch a
bpf script that could then run, with the full set of steps needed to
show it in use.

Also, what would be the value when BPF is not used?

- Arnaldo
 
> Signed-off-by: Brendan Gregg <bgregg@...flix.com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Wang Nan <wangnan0@...wei.com>
> ---
>  include/trace/events/perf.h | 29 +++++++++++++++++++++++++++++
>  kernel/events/core.c        |  5 +++++
>  2 files changed, 34 insertions(+)
>  create mode 100644 include/trace/events/perf.h
> 
> diff --git a/include/trace/events/perf.h b/include/trace/events/perf.h
> new file mode 100644
> index 0000000..461770d
> --- /dev/null
> +++ b/include/trace/events/perf.h
> @@ -0,0 +1,29 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM perf
> +
> +#if !defined(_TRACE_PERF_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_PERF_H
> +
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(perf_hrtimer,
> +	TP_PROTO(struct pt_regs *regs, struct perf_event *event),
> +
> +	TP_ARGS(regs, event),
> +
> +	TP_STRUCT__entry(
> +		__field(struct pt_regs *, regs)
> +		__field(struct perf_event *, event)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->regs = regs;
> +		__entry->event = event;
> +	),
> +
> +	TP_printk("regs=%p evt=%p", __entry->regs, __entry->event)
> +);
> +#endif /* _TRACE_PERF_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 79dae18..0d843a7 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -51,6 +51,9 @@
>  
>  #include <asm/irq_regs.h>
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/perf.h>
> +
>  typedef int (*remote_function_f)(void *);
>  
>  struct remote_function_call {
> @@ -8036,6 +8039,8 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
>  	perf_sample_data_init(&data, 0, event->hw.last_period);
>  	regs = get_irq_regs();
>  
> +	trace_perf_hrtimer(regs, event);
> +
>  	if (regs && !perf_exclude_event(event, regs)) {
>  		if (!(event->attr.exclude_idle && is_idle_task(current)))
>  			if (__perf_event_overflow(event, 1, &data, regs))
> -- 
> 2.7.4