linux-kernel - Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job"

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Message-ID: <20161125131403.GA2813@e106950-lin.cambridge.arm.com>
Date:   Fri, 25 Nov 2016 13:14:03 +0000
From:   Brian Starkey <brian.starkey@....com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let
 ksoftirqd do its job"

Hi,

On Wed, Nov 23, 2016 at 12:03:28PM -0800, Eric Dumazet wrote:
>On Wed, Nov 23, 2016 at 10:21 AM, Brian Starkey <brian.starkey@....com> wrote:
>
>> This patch didn't help.
>>
>> I did get some new traces though - I've attached the diff for the
>> trace_printks I added.
>>
>> Before 4cd13c21b207:
>> https://drive.google.com/open?id=0B8siaK6ZjvEwcEtOeFQzTmY0Nnc
>> After 4cd13c21b207:
>> https://drive.google.com/open?id=0B8siaK6ZjvEwZnQ4MVg1d3d1Tm8
>>
>> It looks like the difference is that after 4cd13c21b207 the RX softirq
>> isn't running, and RX interrupts don't call softirq_raise anymore -
>> presumably because there's one pending, but I didn't have time to
>> track that down to a code-path.
>>
>> Cheers,
>> -Brian
>>
>
>Hi Brian
>
>Looks like netif_rx() drops the incoming packets then ?
>
>Maybe netif_running() is not happy :(
>
>Could you trace netif_rx() return value (NET_RX_SUCCESS or NET_RX_DROP)

Some packets are dropped, but not very many:

   $ grep NET_RX_SUCCESS trace_netif_rx.txt | wc -l
   14399
   $ grep NET_RX_DROP trace_netif_rx.txt | wc -l
   22

Without the ksoftirqd change there were zero NET_RX_DROPs.

-Brian

>
>Thanks !