linux-kernel - Re: ebpf trace doesn't work during cpu hotplug

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Message-ID: <CACVXFVMoi01a2WhF-LWhf3C10Ee5qRXHZjNNMY-Ky+Qk1E4N2Q@mail.gmail.com>
Date:   Mon, 8 Jul 2019 17:43:52 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>, bpf@...r.kernel.org
Subject: Re: ebpf trace doesn't work during cpu hotplug

On Wed, May 29, 2019 at 11:28 AM Ming Lei <tom.leiming@...il.com> wrote:
>
> Hi,
>
> Looks ebpf trace doesn't work during cpu hotplug, see the following trace:
>
> 1) trace two functions called during CPU unplug via bcc/trace
>
> /usr/share/bcc/tools/trace -T 'takedown_cpu "%d", arg1'  'take_cpu_down'
>
> 2) put cpu7 offline via:
>
> echo 0 > /sys/devices/system/cpu/cpu7/online
>
> 3) only trace on 'takedown_cpu' is dumped via bcc/trace:
>
> TIME     PID     TID     COMM            FUNC             -
> 03:23:17 733     733     bash            takedown_cpu     7
>
> The lost trace on 'take_cpu_down' can never be shown, even though
> CPU7 is switched ON again.
>
> take_cpu_down is called via stop_machine_cpuslocked.

>From a user view, I think the tool should be reliable to collect
traces any time.

So ping on this issue...


Thanks,
Ming Lei