netdev - Re: [PATCH 4/5] virtio_net: enable premapped mode for merge and small by default

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Message-ID: <1729824783.098598-5-xuanzhuo@linux.alibaba.com>
Date: Fri, 25 Oct 2024 10:53:03 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org,
 "Michael S. Tsirkin" <mst@...hat.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>,
 virtualization@...ts.linux.dev
Subject: Re: [PATCH 4/5] virtio_net: enable premapped mode for merge and small by default

On Fri, 18 Oct 2024 16:00:07 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Mon, Oct 14, 2024 at 11:12 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> >
> > Currently, the virtio core will perform a dma operation for each
> > buffer. Although, the same page may be operated multiple times.
> >
> > In premapped mod, we can perform only one dma operation for the pages of
> > the alloc frag. This is beneficial for the iommu device.
> >
> > kernel command line: intel_iommu=on iommu.passthrough=0
> >
> >        |  strict=0  | strict=1
> > Before |  775496pps | 428614pps
> > After  | 1109316pps | 742853pps
> >
> > In the 6.11, we disabled this feature because a regress [1].
> >
> > Now, we fix the problem and re-enable it.
> >
> > [1]: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.com
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >  drivers/net/virtio_net.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index cd90e77881df..8cf24b7b58bd 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -6133,6 +6133,21 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
> >         return -ENOMEM;
> >  }
> >
> > +static void virtnet_rq_set_premapped(struct virtnet_info *vi)
> > +{
> > +       int i;
> > +
> > +       /* disable for big mode */
> > +       if (vi->mode == VIRTNET_MODE_BIG)
> > +               return;
>
> Nitpick: I would like such a check to be done at the caller.

I am ok, if you like.

Thanks.


>
> But anyhow the patch looks good
>
> Acked-by: Jason Wang <jasowang@...hat.com>
>
> Thanks
>
> > +
> > +       for (i = 0; i < vi->max_queue_pairs; i++) {
> > +               /* error should never happen */
> > +               BUG_ON(virtqueue_set_dma_premapped(vi->rq[i].vq));
> > +               vi->rq[i].do_dma = true;
> > +       }
> > +}
> > +
> >  static int init_vqs(struct virtnet_info *vi)
> >  {
> >         int ret;
> > @@ -6146,6 +6161,8 @@ static int init_vqs(struct virtnet_info *vi)
> >         if (ret)
> >                 goto err_free;
> >
> > +       virtnet_rq_set_premapped(vi);
> > +
> >         cpus_read_lock();
> >         virtnet_set_affinity(vi);
> >         cpus_read_unlock();
> > --
> > 2.32.0.3.g01195cf9f
> >
>