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Date:   Wed, 6 May 2020 16:37:41 +0800
From:   Jason Wang <>
To:     "Michael S. Tsirkin" <>
        Jesper Dangaard Brouer <>,
        Eugenio Perez Martin <>
Subject: Re: performance bug in virtio net xdp

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 


> The fix is probably to update ewma unconditionally.

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