linux-kernel - Re: [EXPERIENCE] My experience on using perf record BPF filter on a real usecase

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Date:	Tue, 09 Jun 2015 23:42:08 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	"Wangnan (F)" <wangnan0@...wei.com>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	David Ahern <dsahern@...il.com>, He Kuang <hekuang@...wei.com>,
	Jiri Olsa <jolsa@...hat.com>, Kaixu Xia <xiakaixu@...wei.com>,
	Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, pi3orama@....com,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Zefan Li <lizefan@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [EXPERIENCE] My experience on using perf record BPF filter on
 a real usecase

On 6/4/15 3:17 AM, Wangnan (F) wrote:
> Hi all,
>
> I'd like to share my exprience on using 'perf record' BPF filter in a
> real usecase to show the power and shortcome in my patch series:

thanks for sharing!

> Here is another inconvenience. Currently I only concern on write
> syscall issued by iozone. However, without '-a' I'm unable to collect
> information of the locker. If I want to filter sys_{enter,exit}_write
> belong to iozone out using eBPF, I need to implement another function
> like BPF_FUNC_git_comm. Another method is to use perf '--filter' after
> the two events. However it looks strange to use two filter mechanisms
> together. This time I choose to do filtering offline using perf script.

that doesn't sound clean.
btw, I've been playing for a while with
bpf_get_current_task_info() helper:
https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/commit/?id=c5453ffa107ddf95a91920cc947bb8bf9eab16d6
I think it's a better mechanism.
The user can get pid only via:
u32 pid = 0;
bpf_get_current_task_info(&pid, sizeof(pid));
or full pid + comm + future fields via full 'struct bpf_task_info'
Thoughts?

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