On Tue, Dec 20, 2016 at 12:32:40AM +0800, Fam Zheng wrote: > On Mon, 12/19 15:02, Stefan Hajnoczi wrote: > > On Mon, Dec 19, 2016 at 04:51:22PM +0800, Dou Liyang wrote: > > > These patches aim to refactor the qmp_query_blockstats() and > > > improve the performance by reducing the running time of it. > > > > > > qmp_query_blockstats() is used to monitor the blockstats, it > > > querys all the graph_bdrv_states or monitor_block_backends. > > > > > > There are the two jobs: > > > > > > 1 For the performance: > > > > > > 1.1 the time it takes(ns) in each time: > > > the disk numbers | 10 | 500 > > > ------------------------------------- > > > before these patches | 19429 | 667722 > > > after these patches | 17516 | 557044 > > > > > > 1.2 the I/O performance is degraded(%) during the monitor: > > > > > > the disk numbers | 10 | 500 > > > ------------------------------------- > > > before these patches | 1.3 | 14.2 > > > after these patches | 0.8 | 9.1 > > > > Do you know what is consuming the remaining 9.1%? > > > > I'm surprised to see such a high performance impact caused by a QMP > > command. > > If it's "performance is 9.1% worse only during the 557044 ns when the QMP > command is being processed", it's probably becaues the main loop is stalled a > bit, and it's not a big problem. I'd be very surprised if the degradation is > more longer than that.
It would be interesting to compare against virtio-blk dataplane. That
way the QMP command can execute without interfering with disk I/O activity.
qemu-system-x86_64 ... \
-object iothread,id=iothread0 \
-drive if=none,id=drive0,file=vm.img,format=raw,aio=native,cache=none \
-device virtio-blk-pci,drive=drive0,iothread=iothread0
Stefan
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