On Wed, Jul 21, 2021 at 11:42:08AM +0200, Stefano Garzarella wrote: > Since it's a performance regression, if possible we could include it in > 6.1-rc1. > There shouldn't be any particular criticism. > > v1: https://lists.gnu.org/archive/html/qemu-devel/2021-07/msg01526.html > v2: > - s/bacth/batch/ [stefanha] > - limit the batch with the number of available events [stefanha] > - rebased on master > - re-run benchmarks > > Commit 2558cb8dd4 ("linux-aio: increasing MAX_EVENTS to a larger hardcoded > value") changed MAX_EVENTS from 128 to 1024, to increase the number of > in-flight requests. But this change also increased the potential maximum batch > to 1024 elements. > > The problem is noticeable when we have a lot of requests in flight and > multiple > queues attached to the same AIO context. > In this case we potentially create very large batches. Instead, when we have > a single queue, the batch is limited because when the queue is unplugged, > there is a call to io_submit(2). > In practice, io_submit(2) was called only when there are no more queues > plugged > in or when we fill the AIO queue (MAX_EVENTS = 1024). > > This series limit the batch size (number of request submitted to the kernel > through a single io_submit(2) call) in the Linux AIO backend, and add a new > `aio-max-batch` parameter to IOThread to allow tuning it. > If `aio-max-batch` is equal to 0 (default value), the AIO engine will use its > default maximum batch size value. > > I run some benchmarks to choose 32 as default batch value for Linux AIO. > Below the kIOPS measured with fio running in the guest (average over 3 runs): > > | master | with this series applied > | > |143c2e04328| > maxbatch=8|maxbatch=16|maxbatch=32|maxbatch=64| > # queues | 1q | 4qs | 1q | 4qs | 1q | 4qs | 1q | 4qs | 1q | > 4qs | > -- randread tests > -|-----------------------------------------------------------| > bs=4k iodepth=1 | 200 | 195 | 181 | 208 | 200 | 203 | 206 | 212 | 200 | > 204 | > bs=4k iodepth=8 | 269 | 231 | 256 | 244 | 255 | 260 | 266 | 268 | 270 | > 250 | > bs=4k iodepth=64 | 230 | 198 | 262 | 265 | 261 | 253 | 260 | 273 | 253 | > 263 | > bs=4k iodepth=128 | 217 | 181 | 261 | 253 | 249 | 276 | 250 | 278 | 255 | > 278 | > bs=16k iodepth=1 | 130 | 130 | 130 | 130 | 130 | 130 | 137 | 130 | 130 | > 130 | > bs=16k iodepth=8 | 130 | 131 | 130 | 131 | 130 | 130 | 137 | 131 | 131 | > 130 | > bs=16k iodepth=64 | 130 | 102 | 131 | 128 | 131 | 128 | 137 | 140 | 130 | > 128 | > bs=16k iodepth=128 | 131 | 100 | 130 | 128 | 131 | 129 | 137 | 141 | 130 | > 129 | > > 1q = virtio-blk device with a single queue > 4qs = virito-blk device with multi queues (one queue per vCPU - 4) > > I reported only the most significant tests, but I also did other tests to > make sure there were no regressions, here the full report: > https://docs.google.com/spreadsheets/d/11X3_5FJu7pnMTlf4ZatRDvsnU9K3EPj6Mn3aJIsE4tI > > Test environment: > - Disk: Intel Corporation NVMe Datacenter SSD [Optane] > - CPU: Intel(R) Xeon(R) Silver 4214 CPU @ 2.20GHz > - QEMU: qemu-system-x86_64 -machine q35,accel=kvm -smp 4 -m 4096 \ > ... \ > -object iothread,id=iothread0,aio-max-batch=${MAX_BATCH} \ > -device virtio-blk-pci,iothread=iothread0,num-queues=${NUM_QUEUES} > > - benchmark: fio --ioengine=libaio --thread --group_reporting \ > --number_ios=200000 --direct=1 --filename=/dev/vdb \ > --rw=${TEST} --bs=${BS} --iodepth=${IODEPTH} --numjobs=16 > > Next steps: > - benchmark io_uring and use `aio-max-batch` also there > - make MAX_EVENTS parametric adding a new `aio-max-events` parameter > > Thanks, > Stefano > > Stefano Garzarella (3): > iothread: generalize iothread_set_param/iothread_get_param > iothread: add aio-max-batch parameter > linux-aio: limit the batch size using `aio-max-batch` parameter > > qapi/misc.json | 6 ++- > qapi/qom.json | 7 +++- > include/block/aio.h | 12 ++++++ > include/sysemu/iothread.h | 3 ++ > block/linux-aio.c | 9 ++++- > iothread.c | 82 ++++++++++++++++++++++++++++++++++----- > monitor/hmp-cmds.c | 2 + > util/aio-posix.c | 12 ++++++ > util/aio-win32.c | 5 +++ > util/async.c | 2 + > qemu-options.hx | 8 +++- > 11 files changed, 134 insertions(+), 14 deletions(-) > > -- > 2.31.1 >
Thanks, applied to my master tree: https://gitlab.com/stefanha/qemu/commits/master Stefan
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