On Tue, Dec 20, 2016 at 9:54 AM, Dou Liyang <douly.f...@cn.fujitsu.com> wrote: > At 12/20/2016 05:39 PM, Stefan Hajnoczi wrote: >> >> 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. >> > > Yes, I will try to do it for you. > > I have compared against the disk of IDE/SATA, I think the I/O requests > is handled by the vcpu threads. it isn't be disturbed like virtio-blk > dataplane. but its performance also degraded.
IDE/SATA does I/O request *submission* in the vcpu thread. Completion is processed by the main loop. Therefore it is also affected by slow monitor commands. Stefan
