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

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Message-ID: <B352B219-D053-432C-AEB7-C0A74D2F6613@fb.com>
Date:   Mon, 24 Sep 2018 19:30:59 +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 8:30 AM, Eric Dumazet <edumazet@...gle.com> wrote:
> 
> On Sun, Sep 23, 2018 at 10:04 PM David Miller <davem@...emloft.net> wrote:
>> 
>> Series applied, thanks Eric.
> 
> Thanks David.
> 
> Song, would you please this additional patch ?
> 
> diff --git a/net/core/netpoll.c b/net/core/netpoll.c
> index 3219a2932463096566ce8ff336ecdf699422dd65..2ad45babe621b2c979ad5496b7df4342e4efbaa6
> 100644
> --- a/net/core/netpoll.c
> +++ b/net/core/netpoll.c
> @@ -150,13 +150,6 @@ static void poll_one_napi(struct napi_struct *napi)
> {
>        int work = 0;
> 
> -       /* net_rx_action's ->poll() invocations and our's are
> -        * synchronized by this test which is only made while
> -        * holding the napi->poll_lock.
> -        */
> -       if (!test_bit(NAPI_STATE_SCHED, &napi->state))
> -               return;
> -
>        /* If we set this bit but see that it has already been set,
>         * that indicates that napi has been disabled and we need
>         * to abort this operation

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(). So a packet is missed by
napi (set NAPI_STATE_SCHED, but didn't got handled). 

Song