Message-ID: <55494336.4060709@gmail.com>
Date: Tue, 05 May 2015 16:24:54 -0600
From: David Ahern <dsahern@gmail.com>
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To: Rabin Vincent <rabin@rab.in>, Yunlong Song <yunlong.song@huawei.com>
CC: a.p.zijlstra@chello.nl, paulus@samba.org, mingo@redhat.com,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        linux-kernel@vger.kernel.org, wangnan0@huawei.com
Subject: Re: [Question] How does perf still record the stack of a specified
 pid even when that process is interrupted and CPU is scheduled to other process
References: <553A45CA.8020808@huawei.com> <553A4C18.3030609@gmail.com> <553B9F30.1040100@huawei.com> <553BB895.20800@gmail.com> <20150505215328.GA3397@debian>
In-Reply-To: <20150505215328.GA3397@debian>
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On 5/5/15 3:53 PM, Rabin Vincent wrote:
> The commands above will identify the sys_write which takes time but only
> provide the stacktrace at the entry and exit of the syscall, but this do
> not show why the process blocked or what it did inside the system call.
>
> So a way to get what is required for the use case would be to make the
> following changes to the above sequence:
>
> (1) include the sched:* events when perf trace record is run
>
> (2) around the time of interest, look at the kernel stack st the sched:switch
>      events between the entry and the exit.  This will show what the process was
>      waiting for when it when it blocked.  The stacktraces at the
>      stat_runtime events in the process may also be useful to understand what
>      was going on.

agreed.


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