Message-ID: <5577DC40.9020801@plumgrid.com>
Date: Tue, 09 Jun 2015 23:42:08 -0700
From: Alexei Starovoitov <ast@plumgrid.com>
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To: "Wangnan (F)" <wangnan0@huawei.com>, Ingo Molnar <mingo@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
CC: linux-kernel@vger.kernel.org, Adrian Hunter <adrian.hunter@intel.com>,
        Brendan Gregg <brendan.d.gregg@gmail.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        David Ahern <dsahern@gmail.com>, He Kuang <hekuang@huawei.com>,
        Jiri Olsa <jolsa@redhat.com>, Kaixu Xia <xiakaixu@huawei.com>,
        Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Namhyung Kim <namhyung@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, pi3orama@163.com,
        Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
        Zefan Li <lizefan@huawei.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>
Subject: Re: [EXPERIENCE] My experience on using perf record BPF filter on
 a real usecase
References: <1433371238-14572-1-git-send-email-acme@kernel.org> <20150604054854.GA10969@gmail.com> <556FEB32.8040909@huawei.com> <557025A2.6090903@huawei.com>
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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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