Message-ID: <5594B50A.3010705@plumgrid.com>
Date: Wed, 01 Jul 2015 20:50:34 -0700
From: Alexei Starovoitov <ast@plumgrid.com>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0
MIME-Version: 1.0
To: He Kuang <hekuang@huawei.com>, rostedt@goodmis.org,
        masami.hiramatsu.pt@hitachi.com, mingo@redhat.com, acme@redhat.com,
        a.p.zijlstra@chello.nl, jolsa@kernel.org, namhyung@kernel.org
CC: wangnan0@huawei.com, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/5] bpf: Put perf_events check ahead of bpf prog
References: <1435719455-91155-1-git-send-email-hekuang@huawei.com> <1435719455-91155-2-git-send-email-hekuang@huawei.com>
In-Reply-To: <1435719455-91155-2-git-send-email-hekuang@huawei.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1294
Lines: 26

On 6/30/15 7:57 PM, He Kuang wrote:
> When we add a kprobe point and record events by perf, the execution path
> of all threads on each cpu will enter this point, but perf may only
> record events on a particular thread or cpu at this kprobe point, a
> check on call->perf_events list filters out the threads which perf is
> not recording.

I think there is a better way to do that. You're adding artificial
per_cpu filtering whereas you really need per_pid filtering.
The patch kinda worked, but looks more by accident.
The accurate way to do per_pid filtering is to automatically add
'if ((u32)bpf_get_current_pid_tgid() != expected_pid) return 0;'
as the first statement of the program.
You already have nice infra to add prologue to the program.
So I think adding above 'if' on user space side of perf is
a preferred way to achieve that.
Also such per_pid filtering should be smart.
The command 'perf record -a -e my_prog.o -- sleep 10' should
collect all things that my_prog was attached to and not only
things that happened as part of sleep.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/