netdev - Re: [RFC PATCH] virtio_net: XDP support for adjust

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Message-ID: <40812dd8-3fa2-ed85-9c99-d4b22a3d7b31@redhat.com>
Date:   Wed, 4 Jan 2017 11:22:46 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     John Fastabend <john.fastabend@...il.com>, mst@...hat.com
Cc:     john.r.fastabend@...el.com, netdev@...r.kernel.org,
        alexei.starovoitov@...il.com, daniel@...earbox.net
Subject: Re: [RFC PATCH] virtio_net: XDP support for adjust_head



On 2017年01月04日 00:57, John Fastabend wrote:
>>>> +    /* Changing the headroom in buffers is a disruptive operation because
>>>> +     * existing buffers must be flushed and reallocated. This will happen
>>>> +     * when a xdp program is initially added or xdp is disabled by removing
>>>> +     * the xdp program.
>>>> +     */
>>> We probably need reset the device here, but maybe Michale has more ideas. And if
>>> we do this, another interesting thing to do is to disable EWMA and always use a
>>> single page for each packet, this could almost eliminate linearizing.
>> Well with normal MTU 1500 size we should not hit the linearizing case right? The
>> question is should we cap the MTU at GOOD_PACKET_LEN vs the current cap of
>> (PAGE_SIZE - overhead).
> Sorry responding to my own post with a bit more detail. I don't really like
> going to a page for each packet because we end up with double the pages in use
> for the "normal" 1500 MTU case. We could make the xdp allocation scheme smarter
> and allocate a page per packet when MTU is greater than 2k instead of using the
> EWMA but I would push those types of things at net-next and live with the
> linearizing behavior for now or capping the MTU.
>

Yes, agree.

Thanks