linux-kernel - Re: [RFC PATCH 0/4] perf tools: Use the new ability of eBPF programs to access hardware PMU counter

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Date:	Fri, 28 Aug 2015 18:28:33 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Kaixu Xia <xiakaixu@...wei.com>, davem@...emloft.net,
	daniel@...earbox.net, acme@...nel.org, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, masami.hiramatsu.pt@...achi.com,
	jolsa@...nel.org
Cc:	linux-kernel@...r.kernel.org, wangnan0@...wei.com, pi3orama@....com
Subject: Re: [RFC PATCH 0/4] perf tools: Use the new ability of eBPF programs
 to access hardware PMU counter

On 8/27/15 3:42 AM, Kaixu Xia wrote:
> An example is pasted at the bottom of this cover letter. In that example,
> we can get the cpu_cycles and exception taken in sys_write.
>
>   $ cat /sys/kernel/debug/tracing/trace_pipe
>   $ ./perf record --event perf-bpf.o ls
> 	...
>               cat-1653  [003] d..1 88174.613854: : ente:  CPU-3	cyc:48746333	exc:84
>               cat-1653  [003] d..2 88174.613861: : exit:  CPU-3	cyc:48756041	exc:84

nice. probably more complex example that computes the delta of the pmu
counters on the kernel side would be even more interesting.
Do you think you can extend 'perf stat' with a flag that does
stats collection for a given kernel or user function instead of the
whole process ?
Then we can use perf record/report to figure out hot functions and
follow with 'perf stat -f my_hot_func my_process' to drill into
particular function stats.

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