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Date: Thu, 10 Mar 2016 08:48:21 +0200 From: "Michael Rapoport" <RAPOPORT@...ibm.com> To: Greg Kurz <gkurz@...ux.vnet.ibm.com> Cc: borntraeger@...ibm.com, Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, mst@...hat.com, netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org, yang.zhang.wz@...il.com Subject: Re: [PATCH V4 0/3] basic busy polling support for vhost_net Hi Greg, > Greg Kurz <gkurz@...ux.vnet.ibm.com> wrote on 03/09/2016 09:26:45 PM: > > On Fri, 4 Mar 2016 06:24:50 -0500 > > Jason Wang <jasowang@...hat.com> wrote: > > > 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 A were done through: > > > > - 50 us as busy loop timeout > > - Netperf 2.6 > > - Two machines with back to back connected mlx4 > > Hi Jason, > > Could this also improve performance if both VMs are > on the same host system ? I've experimented a little with Jason's patches and guest-to-guest netperf when both guests were on the same host, and I saw improvements for that case. > > - Guest with 1 vcpus and 1 queue > > > > Results: > > - Obvious improvements (%5 - 20%) for latency (TCP_RR). > > - Get a better or minor regression on most of the TX tests, but see > > some regression on 4096 size. > > - Except for 8 sessions of 4096 size RX, have a better or same > > performance. > > - CPU utilization were incrased as expected. > > > > TCP_RR: > > size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/ > > 1/ 1/ +8%/ -32%/ +8%/ +8%/ +7% > > 1/ 50/ +7%/ -19%/ +7%/ +7%/ +1% > > 1/ 100/ +5%/ -21%/ +5%/ +5%/ 0% > > 1/ 200/ +5%/ -21%/ +7%/ +7%/ +1% > > 64/ 1/ +11%/ -29%/ +11%/ +11%/ +10% > > 64/ 50/ +7%/ -19%/ +8%/ +8%/ +2% > > 64/ 100/ +8%/ -18%/ +9%/ +9%/ +2% > > 64/ 200/ +6%/ -19%/ +6%/ +6%/ 0% > > 256/ 1/ +7%/ -33%/ +7%/ +7%/ +6% > > 256/ 50/ +7%/ -18%/ +7%/ +7%/ 0% > > 256/ 100/ +9%/ -18%/ +8%/ +8%/ +2% > > 256/ 200/ +9%/ -18%/ +10%/ +10%/ +3% > > 1024/ 1/ +20%/ -28%/ +20%/ +20%/ +19% > > 1024/ 50/ +8%/ -18%/ +9%/ +9%/ +2% > > 1024/ 100/ +6%/ -19%/ +5%/ +5%/ 0% > > 1024/ 200/ +8%/ -18%/ +9%/ +9%/ +2% > > Guest TX: > > size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/ > > 64/ 1/ -5%/ -28%/ +11%/ +12%/ +10% > > 64/ 4/ -2%/ -26%/ +13%/ +13%/ +13% > > 64/ 8/ -6%/ -29%/ +9%/ +10%/ +10% > > 512/ 1/ +15%/ -7%/ +13%/ +11%/ +3% > > 512/ 4/ +17%/ -6%/ +18%/ +13%/ +11% > > 512/ 8/ +14%/ -7%/ +13%/ +7%/ +7% > > 1024/ 1/ +27%/ -2%/ +26%/ +29%/ +12% > > 1024/ 4/ +8%/ -9%/ +6%/ +1%/ +6% > > 1024/ 8/ +41%/ +12%/ +34%/ +20%/ -3% > > 4096/ 1/ -22%/ -21%/ -36%/ +81%/+1360% > > 4096/ 4/ -57%/ -58%/ +286%/ +15%/+2074% > > 4096/ 8/ +67%/ +70%/ -45%/ -8%/ +63% > > 16384/ 1/ -2%/ -5%/ +5%/ -3%/ +80% > > 16384/ 4/ 0%/ 0%/ 0%/ +4%/ +138% > > 16384/ 8/ 0%/ 0%/ 0%/ +1%/ +41% > > 65535/ 1/ -3%/ -6%/ +2%/ +11%/ +113% > > 65535/ 4/ -2%/ -1%/ -2%/ -3%/ +484% > > 65535/ 8/ 0%/ +1%/ 0%/ +2%/ +40% > > Guest RX: > > size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/ > > 64/ 1/ +31%/ -3%/ +8%/ +8%/ +8% > > 64/ 4/ +11%/ -17%/ +13%/ +14%/ +15% > > 64/ 8/ +4%/ -23%/ +11%/ +11%/ +12% > > 512/ 1/ +24%/ 0%/ +18%/ +14%/ -8% > > 512/ 4/ +4%/ -15%/ +6%/ +5%/ +6% > > 512/ 8/ +26%/ 0%/ +21%/ +10%/ +3% > > 1024/ 1/ +88%/ +47%/ +69%/ +44%/ -30% > > 1024/ 4/ +18%/ -5%/ +19%/ +16%/ +2% > > 1024/ 8/ +15%/ -4%/ +13%/ +8%/ +1% > > 4096/ 1/ -3%/ -5%/ +2%/ -2%/ +41% > > 4096/ 4/ +2%/ +3%/ -20%/ -14%/ -24% > > 4096/ 8/ -43%/ -45%/ +69%/ -24%/ +94% > > 16384/ 1/ -3%/ -11%/ +23%/ +7%/ +42% > > 16384/ 4/ -3%/ -3%/ -4%/ +5%/ +115% > > 16384/ 8/ -1%/ 0%/ -1%/ -3%/ +32% > > 65535/ 1/ +1%/ 0%/ +2%/ 0%/ +66% > > 65535/ 4/ -1%/ -1%/ 0%/ +4%/ +492% > > 65535/ 8/ 0%/ -1%/ -1%/ +4%/ +38% > > > > Changes from V3: > > - drop single_task_running() > > - use cpu_relax_lowlatency() instead of cpu_relax() > > > > Changes from V2: > > - rename vhost_vq_more_avail() to vhost_vq_avail_empty(). And return > > false we __get_user() fails. > > - do not bother premmptions/timers for good path. > > - use vhost_vring_state as ioctl parameter instead of reinveting a new > > one. > > - add the unit of timeout (us) to the comment of new added ioctls > > > > Changes from V1: > > - remove the buggy vq_error() in vhost_vq_more_avail(). > > - leave vhost_enable_notify() untouched. > > > > Changes from RFC V3: > > - small tweak on the code to avoid multiple duplicate conditions in > > critical path when busy loop is not enabled. > > - add the test result of multiple VMs > > > > Changes from RFC 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 RFC 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_avail_empty() > > vhost_net: basic polling support > > > > drivers/vhost/net.c | 78 +++++++++++++++++++++++++++++++++++++++++++--- > > drivers/vhost/vhost.c | 35 +++++++++++++++++++++ > > drivers/vhost/vhost.h | 3 ++ > > include/uapi/linux/vhost.h | 6 ++++ > > 4 files changed, 117 insertions(+), 5 deletions(-) > > >
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