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

Jason Wang
2015-11-12T10:20:25Z

On 11/12/2015 06:16 PM, Jason Wang wrote:
> 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%).

Forget to mention, the following test results by order are:

1) Guest TX
2) Guest RX
3) TCP_RR

> 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(-)
>