On Mon, 19 Aug 2024 18:06:07 -0700, "Si-Wei Liu" <si-wei.liu@xxxxxxxxxx> wrote:
> Hi,
>
> May I know if this is really an intended fix to post officially, or just
> a workaround/probe to make the offset in page_frag happy when
> net_high_order_alloc_disable is true? In case it's the former, even
> though this could fix the issue, I would assume clamping to a smaller
> page_frag than a regular page size for every buffer may have certain
> performance regression for the merge-able buffer case? Can you justify
> the performance impact with some benchmark runs with larger MTU and
> merge-able rx buffers to prove the regression is negligible? You would
> need to compare against where you don't have the inadvertent
> virtnet_rq_dma cost on any page i.e. getting all 4 patches of this
> series reverted. Both tests with net_high_order_alloc_disable set to on
> and off are needed.
I will post a PATCH, let we discuss under that.
Thanks.
>
> Thanks,
> -Siwei
>
> On 8/17/2024 6:20 AM, Xuan Zhuo wrote:
> > Hi, guys, I have a fix patch for this.
> > Could anybody test it?
> >
> > Thanks.
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index af474cc191d0..426d68c2d01d 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -2492,13 +2492,15 @@ static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
> > {
> > struct virtnet_info *vi = rq->vq->vdev->priv;
> > const size_t hdr_len = vi->hdr_len;
> > - unsigned int len;
> > + unsigned int len, max_len;
> > +
> > + max_len = PAGE_SIZE - ALIGN(sizeof(struct virtnet_rq_dma), L1_CACHE_BYTES);
> >
> > if (room)
> > - return PAGE_SIZE - room;
> > + return max_len - room;
> >
> > len = hdr_len + clamp_t(unsigned int, ewma_pkt_len_read(avg_pkt_len),
> > - rq->min_buf_len, PAGE_SIZE - hdr_len);
> > + rq->min_buf_len, max_len - hdr_len);
> >
> > return ALIGN(len, L1_CACHE_BYTES);
> > }
>
