Messages in this thread | | | Subject | Re: Patch "mm, vmstat: make quiet_vmstat lighter" has been added to the 4.4-stable tree | From | Daniel Wagner <> | Date | Wed, 11 Dec 2019 16:54:01 +0100 |
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Hi,
On 2019-12-11 15:46, Greg KH wrote: > On Wed, Dec 11, 2019 at 10:32:49PM +0800, zhangyi (F) wrote: >> We find a performance degradation under lmbench af_unix[1] test case after >> mergeing this patch on my x86 qemu 4.4 machine. The test result is basically >> stable for each teses. >> >> Host machine: CPU: Intel(R) Xeon(R) CPU E5-2690 v3 >> CPU(s): 48 >> MEM: 193047 MB >> >> Guest machine: CPU: QEMU Virtual CPU version 2.5+ >> CPU(s): 8 >> MEM: 26065 MB >> >> Before this patch: >> [root@localhost ~]# lmbench-3.0-a9/bin/x86_64-linux-gnu/lat_unix -P 1 >> AF_UNIX sock stream latency: 133.7073 microseconds >> >> After this patch: >> [root@localhost ~]# lmbench-3.0-a9/bin/x86_64-linux-gnu/lat_unix -P 1 >> AF_UNIX sock stream latency: 156.4722 microseconds >> >> If we set task to a constant cpu, the degradation does not appear. >> >> Before this patch: >> [root@localhost ~]# lmbench-3.0-a9/bin/x86_64-linux-gnu/lat_unix -P 1 >> AF_UNIX sock stream latency: 17.9296 microseconds >> >> After this patch: >> [root@localhost ~]# lmbench-3.0-a9/bin/x86_64-linux-gnu/lat_unix -P 1 >> AF_UNIX sock stream latency: 17.7500 microseconds >> >> We also test it on the aarch64 hi1215 machine with 8 cpu cores. >> >> Before this patch: >> [root@localhost ~]# ./lat_unix -P 1 >> AF_UNIX sock stream latency: 30.7 microseconds >> >> After this patch: >> [root@localhost ~]# ./lat_unix -P 1 >> AF_UNIX sock stream latency: 37.5 microseconds >> >> Accessories included my reproduce config for x86 qemu. Any thoughts? > > This fixes a bug, as reported by Daniel Wagner. So it's probably better > to have a stable system instead of a broken one, right? :) > > Daniel can provide more information if needed.
IIRC, this patch got necessary because bdf3c006b9a2 ("vmstat: make vmstat_updater deferrable again and shut down on idle") was added to stable. Without it v4.4-rt is not working at all.
> What about when you run your tests on a 4.9 or newer kernel that > already has this integrated?
That said, I was going through all changes in vmstat.c upstream and we backported almost all changes to v4.4 at that point. So if this is a really giving you a performance hit, I suspect you would see it upstream as well.
Thanks, Daniel
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