Re: Patch "mm, vmstat: make quiet_vmstat lighter" has been added to the 4.4-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Dec 11, 2019 at 10:32:49PM +0800, zhangyi (F) wrote:
> Hi, all
> 
> 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.

What about when you run your tests on a 4.9 or newer kernel that already
has this integrated?

thanks,

greg k-h