From: "Zhangjie (HZ)" <[email protected]>
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 <[email protected]>
Applied.
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