netdev - Re: [net-next PATCH v2 0/5] XDP adjust head support for virtio

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Date:   Mon, 6 Feb 2017 15:12:17 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        David Miller <davem@...emloft.net>
Cc:     john.fastabend@...il.com, kubakici@...pl, ast@...com,
        john.r.fastabend@...el.com, netdev@...r.kernel.org
Subject: Re: [net-next PATCH v2 0/5] XDP adjust head support for virtio



On 2017年02月06日 12:39, Michael S. Tsirkin wrote:
> On Sun, Feb 05, 2017 at 05:36:34PM -0500, David Miller wrote:
>> From: John Fastabend <john.fastabend@...il.com>
>> Date: Thu, 02 Feb 2017 19:14:05 -0800
>>
>>> This series adds adjust head support for virtio. The following is my
>>> test setup. I use qemu + virtio as follows,
>>>
>>> ./x86_64-softmmu/qemu-system-x86_64 \
>>>    -hda /var/lib/libvirt/images/Fedora-test0.img \
>>>    -m 4096  -enable-kvm -smp 2 -netdev tap,id=hn0,queues=4,vhost=on \
>>>    -device virtio-net-pci,netdev=hn0,mq=on,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off,vectors=9
>>>
>>> In order to use XDP with virtio until LRO is supported TSO must be
>>> turned off in the host. The important fields in the above command line
>>> are the following,
>>>
>>>    guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
>>>
>>> Also note it is possible to conusme more queues than can be supported
>>> because when XDP is enabled for retransmit XDP attempts to use a queue
>>> per cpu. My standard queue count is 'queues=4'.
>>>
>>> After loading the VM I run the relevant XDP test programs in,
>>>
>>>    ./sammples/bpf
>>>
>>> For this series I tested xdp1, xdp2, and xdp_tx_iptunnel. I usually test
>>> with iperf (-d option to get bidirectional traffic), ping, and pktgen.
>>> I also have a modified xdp1 that returns XDP_PASS on any packet to ensure
>>> the normal traffic path to the stack continues to work with XDP loaded.
>>>
>>> It would be great to automate this soon. At the moment I do it by hand
>>> which is starting to get tedious.
>>>
>>> v2: original series dropped trace points after merge.
>> Michael, I just want to apply this right now.
>>
>> I don't think haggling over whether to allocate the adjust_head area
>> unconditionally or not is a blocker for this series going in.  That
>> can be addressed trivially in a follow-on patch.
> FYI it would just mean we revert most of this patchset except patches 2 and 3 though.
>
>> We want these new reset paths tested as much as possible and each day
>> we delay this series is detrimental towards that goal.
>>
>> Thanks.
> Well the point is to avoid resets completely, at the cost of extra 256 bytes
> for packets > 128 bytes on ppc (64k pages) only.
>
> Found a volunteer so I hope to have this idea tested on ppc Tuesday.
>
> And really all we need to know is confirm whether this:
> -#define MERGEABLE_BUFFER_MIN_ALIGN_SHIFT ((PAGE_SHIFT + 1) / 2)
> +#define MERGEABLE_BUFFER_MIN_ALIGN_SHIFT (PAGE_SHIFT / 2 + 1)
>
> affects performance in a measureable way.

Ok, but we still need to drop some packets with this way I believe, and 
does it work if we allow to change the size of headroom in the future?

Thanks

>
> So I would rather wait another day. But the patches themselves
> look correct, from that POV.
>
> Acked-by: Michael S. Tsirkin <mst@...hat.com>
>
> but I would prefer that you waited another day for a Tested-by from me too.
>