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From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Jakub Kicinski <kuba@kernel.org>, Wei Wang <weiwan@google.com>,
	David Miller <davem@davemloft.net>,
	Network Development <netdev@vger.kernel.org>,
	virtualization <virtualization@lists.linux-foundation.org>,
	Jason Wang <jasowang@redhat.com>
Subject: Re: [PATCH v3 4/4] virtio_net: disable cb aggressively
Date: Wed, 26 May 2021 17:22:08 -0400	[thread overview]
Message-ID: <CA+FuTSetvnwCzyuFkypkXgYycsMe1B3brW93upmg+KjGsgD-gA@mail.gmail.com> (raw)
In-Reply-To: <18b47c22-8c8a-7699-ffaf-ccfdcbf39d37@gmail.com>

On Wed, May 26, 2021 at 11:15 AM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
>
>
> On 5/26/21 10:24 AM, Michael S. Tsirkin wrote:
> > There are currently two cases where we poll TX vq not in response to a
> > callback: start xmit and rx napi.  We currently do this with callbacks
> > enabled which can cause extra interrupts from the card.  Used not to be
> > a big issue as we run with interrupts disabled but that is no longer the
> > case, and in some cases the rate of spurious interrupts is so high
> > linux detects this and actually kills the interrupt.

Temporarily disabling interrupts during free_old_xmit_skbs in
virtnet_poll_cleantx might reduce the spurious interrupt rate by
avoiding an additional Tx interrupt from being scheduled during
virtnet_poll_cleantx.

It probably does not address all spurious interrupts, as
virtnet_poll_cleantx might also run in between the scheduling of the
Tx interrupt and the call to virtnet_poll_tx, right? The Tx and Rx
interrupts racing.

If I can reproduce the report, I can also test how much this helps in practice.

> > Fix up by disabling the callbacks before polling the tx vq.
>
>
> It is not clear why we want to poll TX completions from ndo_start_xmit() in napi mode ?

Yes, we can simply exclude that. The original napi-tx patch did not
make that change, but not for any strong reason.

WARNING: multiple messages have this Message-ID (diff)
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	Network Development <netdev@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	virtualization <virtualization@lists.linux-foundation.org>,
	Jakub Kicinski <kuba@kernel.org>, Wei Wang <weiwan@google.com>,
	David Miller <davem@davemloft.net>
Subject: Re: [PATCH v3 4/4] virtio_net: disable cb aggressively
Date: Wed, 26 May 2021 17:22:08 -0400	[thread overview]
Message-ID: <CA+FuTSetvnwCzyuFkypkXgYycsMe1B3brW93upmg+KjGsgD-gA@mail.gmail.com> (raw)
In-Reply-To: <18b47c22-8c8a-7699-ffaf-ccfdcbf39d37@gmail.com>

On Wed, May 26, 2021 at 11:15 AM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
>
>
> On 5/26/21 10:24 AM, Michael S. Tsirkin wrote:
> > There are currently two cases where we poll TX vq not in response to a
> > callback: start xmit and rx napi.  We currently do this with callbacks
> > enabled which can cause extra interrupts from the card.  Used not to be
> > a big issue as we run with interrupts disabled but that is no longer the
> > case, and in some cases the rate of spurious interrupts is so high
> > linux detects this and actually kills the interrupt.

Temporarily disabling interrupts during free_old_xmit_skbs in
virtnet_poll_cleantx might reduce the spurious interrupt rate by
avoiding an additional Tx interrupt from being scheduled during
virtnet_poll_cleantx.

It probably does not address all spurious interrupts, as
virtnet_poll_cleantx might also run in between the scheduling of the
Tx interrupt and the call to virtnet_poll_tx, right? The Tx and Rx
interrupts racing.

If I can reproduce the report, I can also test how much this helps in practice.

> > Fix up by disabling the callbacks before polling the tx vq.
>
>
> It is not clear why we want to poll TX completions from ndo_start_xmit() in napi mode ?

Yes, we can simply exclude that. The original napi-tx patch did not
make that change, but not for any strong reason.
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

  reply	other threads:[~2021-05-26 21:22 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-26  8:24 [PATCH v3 0/4] virtio net: spurious interrupt related fixes Michael S. Tsirkin
2021-05-26  8:24 ` Michael S. Tsirkin
2021-05-26  8:24 ` [PATCH v3 1/4] virtio_net: move tx vq operation under tx queue lock Michael S. Tsirkin
2021-05-26  8:24   ` Michael S. Tsirkin
2021-05-27  3:41   ` Jason Wang
2021-05-27  3:41     ` Jason Wang
2021-05-28 22:25     ` Willem de Bruijn
2021-05-28 22:25       ` Willem de Bruijn
2021-06-09 22:03       ` Michael S. Tsirkin
2021-06-09 22:03         ` Michael S. Tsirkin
2021-05-26  8:24 ` [PATCH v3 2/4] virtio_net: move txq wakeups under tx q lock Michael S. Tsirkin
2021-05-26  8:24   ` Michael S. Tsirkin
2021-05-27  3:48   ` Jason Wang
2021-05-27  3:48     ` Jason Wang
2021-05-26  8:24 ` [PATCH v3 3/4] virtio: fix up virtio_disable_cb Michael S. Tsirkin
2021-05-26  8:24   ` Michael S. Tsirkin
2021-05-27  4:01   ` Jason Wang
2021-05-27  4:01     ` Jason Wang
2023-03-30  6:07   ` Xuan Zhuo
2023-03-30  6:07     ` Xuan Zhuo
2023-03-30  6:44     ` Michael S. Tsirkin
2023-03-30  6:44       ` Michael S. Tsirkin
2023-03-30  6:54       ` Xuan Zhuo
2023-03-30  6:54         ` Xuan Zhuo
2023-03-30 14:04         ` Michael S. Tsirkin
2023-03-30 14:04           ` Michael S. Tsirkin
2023-03-31  3:38           ` Xuan Zhuo
2023-03-31  3:38             ` Xuan Zhuo
2021-05-26  8:24 ` [PATCH v3 4/4] virtio_net: disable cb aggressively Michael S. Tsirkin
2021-05-26  8:24   ` Michael S. Tsirkin
2021-05-26 15:15   ` Eric Dumazet
2021-05-26 15:15     ` Eric Dumazet
2021-05-26 21:22     ` Willem de Bruijn [this message]
2021-05-26 21:22       ` Willem de Bruijn
2021-05-26 19:39   ` Jakub Kicinski
2021-05-27  4:09   ` Jason Wang
2021-05-27  4:09     ` Jason Wang
2023-01-16 13:41   ` Laurent Vivier
2023-01-16 13:41     ` Laurent Vivier
2023-01-17  3:48     ` Jason Wang
2023-01-17  3:48       ` Jason Wang
2021-05-26 15:34 ` [PATCH v3 0/4] virtio net: spurious interrupt related fixes Willem de Bruijn
2021-05-26 15:34   ` Willem de Bruijn
2021-06-01  2:53   ` Willem de Bruijn
2021-06-01  2:53     ` Willem de Bruijn
2021-06-09 21:36     ` Willem de Bruijn
2021-06-09 21:36       ` Willem de Bruijn
2021-06-09 22:59       ` Willem de Bruijn
2021-06-09 22:59         ` Willem de Bruijn

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