[PATCH net-next RFC V3 0/3] basic busy polling support for vhost_net

Jason Wang
2015-11-12T10:16:32Z

Hi all:

This series tries to add basic busy polling for vhost net. The idea is
simple: at the end of tx/rx processing, busy polling for new tx added
descriptor and rx receive socket for a while. The maximum number of
time (in us) could be spent on busy polling was specified ioctl.

Test were done through:

- 50 us as busy loop timeout
- Netperf 2.6
- Two machines with back to back connected ixgbe
- Guest with 1 vcpu and 1 queue

Results:
- For stream workload, ioexits were reduced dramatically in medium
size (1024-2048) of tx (at most -39%) and almost all rx (at most
-79%) as a result of polling. This compensate for the possible
wasted cpu cycles more or less. That porbably why we can still see
some increasing in the normalized throughput in some cases.
- Throughput of tx were increased (at most 105%) expect for the huge
write (16384). And we can send more packets in the case (+tpkts were
increased).
- Very minor rx regression in some cases.
- Improvemnt on TCP_RR (at most 16%).

size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
64/ 1/ +9%/ -17%/ +5%/ +10%/ -2%
64/ 2/ +8%/ -18%/ +6%/ +10%/ -1%
64/ 4/ +4%/ -21%/ +6%/ +10%/ -1%
64/ 8/ +9%/ -17%/ +6%/ +9%/ -2%
256/ 1/ +20%/ -1%/ +15%/ +11%/ -9%
256/ 2/ +15%/ -6%/ +15%/ +8%/ -8%
256/ 4/ +17%/ -4%/ +16%/ +8%/ -8%
256/ 8/ -61%/ -69%/ +16%/ +10%/ -10%
512/ 1/ +15%/ -3%/ +19%/ +18%/ -11%
512/ 2/ +19%/ 0%/ +19%/ +13%/ -10%
512/ 4/ +18%/ -2%/ +18%/ +15%/ -10%
512/ 8/ +17%/ -1%/ +18%/ +15%/ -11%
1024/ 1/ +25%/ +4%/ +27%/ +16%/ -21%
1024/ 2/ +28%/ +8%/ +25%/ +15%/ -22%
1024/ 4/ +25%/ +5%/ +25%/ +14%/ -21%
1024/ 8/ +27%/ +7%/ +25%/ +16%/ -21%
2048/ 1/ +32%/ +12%/ +31%/ +22%/ -38%
2048/ 2/ +33%/ +12%/ +30%/ +23%/ -36%
2048/ 4/ +31%/ +10%/ +31%/ +24%/ -37%
2048/ 8/ +105%/ +75%/ +33%/ +23%/ -39%
16384/ 1/ 0%/ -14%/ +2%/ 0%/ +19%
16384/ 2/ 0%/ -13%/ +19%/ -13%/ +17%
16384/ 4/ 0%/ -12%/ +3%/ 0%/ +2%
16384/ 8/ 0%/ -11%/ -2%/ +1%/ +1%
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
64/ 1/ -7%/ -23%/ +4%/ +6%/ -74%
64/ 2/ -2%/ -12%/ +2%/ +2%/ -55%
64/ 4/ +2%/ -5%/ +10%/ -2%/ -43%
64/ 8/ -5%/ -5%/ +11%/ -34%/ -59%
256/ 1/ -6%/ -16%/ +9%/ +11%/ -60%
256/ 2/ +3%/ -4%/ +6%/ -3%/ -28%
256/ 4/ 0%/ -5%/ -9%/ -9%/ -10%
256/ 8/ -3%/ -6%/ -12%/ -9%/ -40%
512/ 1/ -4%/ -17%/ -10%/ +21%/ -34%
512/ 2/ 0%/ -9%/ -14%/ -3%/ -30%
512/ 4/ 0%/ -4%/ -18%/ -12%/ -4%
512/ 8/ -1%/ -4%/ -1%/ -5%/ +4%
1024/ 1/ 0%/ -16%/ +12%/ +11%/ -10%
1024/ 2/ 0%/ -11%/ 0%/ +5%/ -31%
1024/ 4/ 0%/ -4%/ -7%/ +1%/ -22%
1024/ 8/ -5%/ -6%/ -17%/ -29%/ -79%
2048/ 1/ 0%/ -16%/ +1%/ +9%/ -10%
2048/ 2/ 0%/ -12%/ +7%/ +9%/ -26%
2048/ 4/ 0%/ -7%/ -4%/ +3%/ -64%
2048/ 8/ -1%/ -5%/ -6%/ +4%/ -20%
16384/ 1/ 0%/ -12%/ +11%/ +7%/ -20%
16384/ 2/ 0%/ -7%/ +1%/ +5%/ -26%
16384/ 4/ 0%/ -5%/ +12%/ +22%/ -23%
16384/ 8/ 0%/ -1%/ -8%/ +5%/ -3%
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
1/ 1/ +9%/ -29%/ +9%/ +9%/ +9%
1/ 25/ +6%/ -18%/ +6%/ +6%/ -1%
1/ 50/ +6%/ -19%/ +5%/ +5%/ -2%
1/ 100/ +5%/ -19%/ +4%/ +4%/ -3%
64/ 1/ +10%/ -28%/ +10%/ +10%/ +10%
64/ 25/ +8%/ -18%/ +7%/ +7%/ -2%
64/ 50/ +8%/ -17%/ +8%/ +8%/ -1%
64/ 100/ +8%/ -17%/ +8%/ +8%/ -1%
256/ 1/ +10%/ -28%/ +10%/ +10%/ +10%
256/ 25/ +15%/ -13%/ +15%/ +15%/ 0%
256/ 50/ +16%/ -14%/ +18%/ +18%/ +2%
256/ 100/ +15%/ -13%/ +12%/ +12%/ -2%

Changes from V2:
- poll also at the end of rx handling
- factor out the polling logic and optimize the code a little bit
- add two ioctls to get and set the busy poll timeout
- test on ixgbe (which can give more stable and reproducable numbers)
instead of mlx4.

Changes from V1:
- Add a comment for vhost_has_work() to explain why it could be
lockless
- Add param description for busyloop_timeout
- Split out the busy polling logic into a new helper
- Check and exit the loop when there's a pending signal
- Disable preemption during busy looping to make sure lock_clock() was
correctly used.

Jason Wang (3):
vhost: introduce vhost_has_work()
vhost: introduce vhost_vq_more_avail()
vhost_net: basic polling support

drivers/vhost/net.c | 77 +++++++++++++++++++++++++++++++++++++++++++---
drivers/vhost/vhost.c | 48 +++++++++++++++++++++++------
drivers/vhost/vhost.h | 3 ++
include/uapi/linux/vhost.h | 11 +++++++
4 files changed, 125 insertions(+), 14 deletions(-)

--
2.1.4