netdev - Re: [PATCH net 00/15] netpoll: avoid capture effects for NAPI drivers

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Message-ID: <ED77932E-558E-4422-AA7C-2DEED4F2954C@fb.com>
Date:   Mon, 24 Sep 2018 20:00:34 +0000
From:   Song Liu <songliubraving@...com>
To:     Eric Dumazet <edumazet@...gle.com>
CC:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        "michael.chan@...adcom.com" <michael.chan@...adcom.com>,
        Ariel Elior <ariel.elior@...ium.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH net 00/15] netpoll: avoid capture effects for NAPI drivers



> On Sep 24, 2018, at 12:41 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> 
> On Mon, Sep 24, 2018 at 12:31 PM Song Liu <songliubraving@...com> wrote:
> 
>> This triggers dev_watchdog() on a simple netperf TCP_RR on bnxt (I haven't
>> tested other drivers yet).
>> 
>> I guess this is because NAPI_STATE_SCHED is set when poll_one_napi() calls
>> napi->poll(). And then cleared by napi->poll().
> 
> Which part of napi->poll() could possibly clear NAPI_STATE_SCHED when
> called by netpoll ?
> 
> AFAIK, napi_complete_done() should exit early (before having a chance
> to clear NAPI_STATE_SCHED)
> because of :
> 
> if (unlikely(n->state & (NAPIF_STATE_NPSVC | NAPIF_STATE_IN_BUSY_POLL)))
>     return false;
> 
> Thanks !

You are right on this condition. But this does trigger dev_watchdog() for
some reason. 

Thanks,
Song