linux-kernel - Re: [PATCH net v2 2/2] tuntap: correctly add the missing xdp flush

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Message-ID: <0bb9796e-5f52-dc9a-b7c2-6628bca712ed@cogentembedded.com>
Date:   Thu, 22 Feb 2018 10:54:30 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     mst@...hat.com, christoffer.dall@...aro.org
Subject: Re: [PATCH net v2 2/2] tuntap: correctly add the missing xdp flush

Hello!

On 2/22/2018 9:24 AM, Jason Wang wrote:

> Commit 762c330d670e ("tuntap: add missing xdp flush") tries to fix the
> devmap stall caused by missed xdp flush by counting the pending xdp
> redirected packets and flush when it exceeds NAPI_POLL_WEIGHT or
> MSG_MORE is clear. This may lead BUG() since xdp_do_flush() was

    Lead to BUG().

> called under process context with preemption enabled. Simply disable

    s/under/in the/?

> preemption may silent the warning but be not enough since process may

    Silence.

> move between different CPUS during a batch which cause xdp_do_flush()
> misses some CPU where the process run previously. Consider the several
> fallouts, that commit was reverted. To fix the issue correctly, we can
> simply calling xdp_do_flush() immediately after xdp_do_redirect(),

    Call.

> a side effect is that this removes any possibility of batching which
> could be addressed in the future.
> 
> Reported-by: Christoffer Dall <christoffer.dall@...aro.org>
> Fixes: 762c330d670e ("tuntap: add missing xdp flush")
> Signed-off-by: Jason Wang <jasowang@...hat.com>
[...]

MBR, Sergei