From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org, Jesper Dangaard Brouer <brouer@redhat.com>,
Eugenio Perez Martin <eperezma@redhat.com>
Subject: Re: performance bug in virtio net xdp
Date: Wed, 6 May 2020 07:57:41 -0400 [thread overview]
Message-ID: <20200506075719-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <7d801479-5572-0031-b306-a735ca4ce0e4@redhat.com>
On Wed, May 06, 2020 at 04:37:41PM +0800, Jason Wang wrote:
>
> On 2020/5/6 下午4:08, Michael S. Tsirkin wrote:
> > So for mergeable bufs, we use ewma machinery to guess the correct buffer
> > size. If we don't guess correctly, XDP has to do aggressive copies.
> >
> > Problem is, xdp paths do not update the ewma at all, except
> > sometimes with XDP_PASS. So whatever we happen to have
> > before we attach XDP, will mostly stay around.
>
>
> It looks ok to me since we always use PAGE_SIZE when XDP is enabled in
> get_mergeable_buf_len()?
>
> Thanks
>
Oh right. Good point! Answered in another thread.
> >
> > The fix is probably to update ewma unconditionally.
> >
next prev parent reply other threads:[~2020-05-06 11:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-06 8:08 performance bug in virtio net xdp Michael S. Tsirkin
2020-05-06 8:37 ` Jason Wang
2020-05-06 11:57 ` Michael S. Tsirkin [this message]
2020-05-06 8:37 ` Jesper Dangaard Brouer
2020-05-06 11:57 ` Michael S. Tsirkin
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