[PATCH v2 net-next 0/4] vhost_net: Avoid vq kicks during busyloop

Toshiaki Makita
2018-07-03T07:31:30Z

Under heavy load vhost tx busypoll tend not to suppress vq kicks, which
causes poor guest tx performance. The detailed scenario is described in
commitlog of patch 2.
Rx seems not to have that serious problem, but for consistency I made a
similar change on rx to avoid rx wakeups (patch 3).
Additionary patch 4 is to avoid rx kicks under heavy load during
busypoll.

Tx performance is greatly improved by this change. I don't see notable
performance change on rx with this series though.

Performance numbers (tx):

- Bulk transfer from guest to external physical server.
[Guest]->vhost_net->tap--(XDP_REDIRECT)-->i40e --(wire)--> [Server]
- Set 10us busypoll.
- Guest disables checksum and TSO because of host XDP.
- Measured single flow Mbps by netperf, and kicks by perf kvm stat
(EPT_MISCONFIG event).

Before After
Mbps kicks/s Mbps kicks/s
UDP_STREAM 1472byte 247758 27
Send 3645.37 6958.10
Recv 3588.56 6958.10
1byte 9865 37
Send 4.34 5.43
Recv 4.17 5.26
TCP_STREAM 8801.03 45794 9592.77 2884

v2:
- Split patches into 3 parts (renaming variables, tx-kick fix, rx-wakeup
fix).
- Avoid rx-kicks too (patch 4).
- Don't memorize endtime as it is not needed for now.

Toshiaki Makita (4):
vhost_net: Rename local variables in vhost_net_rx_peek_head_len
vhost_net: Avoid tx vring kicks during busyloop
vhost_net: Avoid rx queue wake-ups during busypoll
vhost_net: Avoid rx vring kicks during busyloop

drivers/vhost/net.c | 95 +++++++++++++++++++++++++++++++++--------------------
1 file changed, 60 insertions(+), 35 deletions(-)

--
1.8.3.1