virtio-net: Set needed_headroom for virtio-net when VIRTIO_F_ANY_LAYOUT is true
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>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed