netdev - Re: [PATCH net-next v4 0/5] virtio_net: enable the irq for ctrlq

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Date: Thu, 20 Jun 2024 15:16:20 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: netdev@...r.kernel.org,
 virtualization@...ts.linux.dev,
 Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v4 0/5] virtio_net: enable the irq for ctrlq

On Wed, 19 Jun 2024 17:16:57 -0400, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Thu, Jun 20, 2024 at 12:19:03AM +0800, Heng Qi wrote:
> > Ctrlq in polling mode may cause the virtual machine to hang and
> > occupy additional CPU resources. Enabling the irq for ctrlq
> > alleviates this problem and allows commands to be requested
> > concurrently.
> 
> Any patch that is supposed to be a performance improvement
> has to come with actual before/after testing restults, not
> vague "may cause".

1. If the device does not respond in time, the CPU usage for ctrlq in the polling mode is
   ~100%, and in irq mode is ~0%;
2. If there are concurrent requests, the situation in 1 will be even worse;
3. On 64 queues with dim on, use nginx + wrk with the number of connections is 500:
   a. If ctrlq is in polling mode and concurrent requests are not supported:
      seeing that the dim worker occupies 20%+ CPU usage. Because of the
      large number of queues, dim requests cannot be concurrent, and the
      performance is unstable;
   b. If ctrlq is in irq mode and concurrent requests are supported: the overhead
      of the dim worker is not visible, and the pps increases by ~13%
      compared to a.

Thanks.

> 
> 
> 
> > Changelog
> > =========
> > v3->v4:
> >   - Turn off the switch before flush the get_cvq work.
> >   - Add interrupt suppression.
> > 
> > v2->v3:
> >   - Use the completion for dim cmds.
> > 
> > v1->v2:
> >   - Refactor the patch 1 and rephase the commit log.
> > 
> > Heng Qi (5):
> >   virtio_net: passing control_buf explicitly
> >   virtio_net: enable irq for the control vq
> >   virtio_net: change the command token to completion
> >   virtio_net: refactor command sending and response handling
> >   virtio_net: improve dim command request efficiency
> > 
> >  drivers/net/virtio_net.c | 309 ++++++++++++++++++++++++++++++++-------
> >  1 file changed, 260 insertions(+), 49 deletions(-)
> > 
> > -- 
> > 2.32.0.3.g01195cf9f
>