Messages in this thread | | | Date | Wed, 30 Apr 2014 13:32:28 -0400 (EDT) | Subject | Re: [PATCH net-next] virtio-net: Set needed_headroom for virtio-net when VIRTIO_F_ANY_LAYOUT is true | From | David Miller <> |
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From: "Zhangjie (HZ)" <zhangjie14@huawei.com> Date: Tue, 29 Apr 2014 18:43:22 +0800
> This is a small supplement for commit e7428e95a06fb516fac1308bd0e176e27c0b9287 > ("virtio-net: put virtio-net header inline with data"). TCP packages have > enough room to put virtio-net header in, but UDP packages do not. By > setting dev->needed_headroom for virtio-net device, UDP packages could have > enough room. > > For UDP packages, sk_buff is alloced in fun __ip_append_data. The size is > "alloclen + hh_len + 15", and "hh_len = LL_RESERVED_SPACE(rt-dst.dev);". > The Macro is defined as follows: > #define LL_RESERVED_SPACE(dev) \ > ((((dev)->hard_header_len+(dev)->needed_headroom)\ > &~(HH_DATA_MOD - 1)) + HH_DATA_MOD) > By default, for UDP packages, after skb is allocated, only 16 bytes > reserved. And 2 bytes remained after mac header is set. That is not enough > to put virtio-net header in. If we set dev->needed_headroom to 12 or 10 > (according to mergeable_rx_bufs is on or off ), more room can be reserved. > Then there is enough room for UDP packages to put the header in. > > test result list as below: > guest and host: suse11sp3, netperf, intel 2.4GHz > +-------+---------+---------+---------+---------+ > | | old | new | > +-------+---------+---------+---------+---------+ > | UDP | Gbit/s | pps | Gbit/s | pps | > | 64 | 0.57 | 692232 | 0.61 | 742420 | > | 256 | 1.60 | 686860 | 1.71 | 733331 | > | 512 | 2.92 | 674576 | 3.07 | 710446 | > | 1024 | 4.99 | 598977 | 5.17 | 620821 | > | 1460 | 5.68 | 483757 | 7.16 | 610519 | > | 4096 | 6.98 | 637468 | 7.21 | 658471 | > +-------+---------+---------+---------+---------+ > > Signed-off-by: Zhang Jie <zhangjie14@huawei.com>
Applied.
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