Re: [morse:mpam/move_to_fs/v7_bare] [x86/resctrl] 0021800a46: will-it-scale.per_process_ops 18.4% improvement

[Oliver Sang]

hi, Reinette,

On Mon, Mar 10, 2025 at 02:17:51PM -0700, Reinette Chatre wrote:
> Hi,
> 
> On 3/10/25 7:06 AM, kernel test robot wrote:
> > 
> > 
> > Hello,
> > 
> > kernel test robot noticed a 18.4% improvement of will-it-scale.per_process_ops on:
> > 
> > 
> > commit: 0021800a465d495a536265c52f8a031da43948ed ("x86/resctrl: Use schema type to determine the schema format string")
> > https://git.kernel.org/cgit/linux/kernel/git/morse/linux.git mpam/move_to_fs/v7_bare
> > 
> > testcase: will-it-scale
> > config: x86_64-rhel-9.4
> > compiler: gcc-12
> > test machine: 224 threads 2 sockets Intel(R) Xeon(R) Platinum 8480CTDX (Sapphire Rapids) with 512G memory
> > parameters:
> > 
> > 	nr_task: 100%
> > 	mode: process
> > 	test: signal1
> > 	cpufreq_governor: performance
> > 
> > 
> > In addition to that, the commit also has significant impact on the following tests:
> > 
> > +------------------+---------------------------------------------------------------------------------------------+
> > | testcase: change | stress-ng: stress-ng.usersyscall.ops_per_sec 18.0% improvement                              |
> > | test machine     | 224 threads 2 sockets Intel(R) Xeon(R) Platinum 8480CTDX (Sapphire Rapids) with 512G memory |
> > | test parameters  | cpufreq_governor=performance                                                                |
> > |                  | nr_threads=100%                                                                             |
> > |                  | test=usersyscall                                                                            |
> > |                  | testtime=60s                                                                                |
> > +------------------+---------------------------------------------------------------------------------------------+
> > 
> > 
> > 
> > 
> > Details are as below:
> > -------------------------------------------------------------------------------------------------->
> > 
> > 
> > The kernel config and materials to reproduce are available at:
> > https://download.01.org/0day-ci/archive/20250310/202503102156.d70c4800-lkp@xxxxxxxxx
> > 
> > =========================================================================================
> > compiler/cpufreq_governor/kconfig/mode/nr_task/rootfs/tbox_group/test/testcase:
> >   gcc-12/performance/x86_64-rhel-9.4/process/100%/debian-12-x86_64-20240206.cgz/lkp-spr-2sp4/signal1/will-it-scale
> > 
> > commit: 
> >   a13ae432a6 ("x86/resctrl: Use schema type to determine how to parse schema values")
> >   0021800a46 ("x86/resctrl: Use schema type to determine the schema format string")
> > 
> 
> It is surprising to me that these commits make a difference in these workloads. I searched around for resctrl in
> https://github.com/intel/lkp-tests but is seems as though it runs the resctrl selftests only and do not
> use resctrl as part of any tests reported here. From what I understand, by not even mounting resctrl, these tests
> (a) do not exercise these code paths, and (b) do not use resctrl to control resources allocated for these workloads. 

thanks a lot for education! this could be an alignment issue.

since we found similar performanance impacts on different cases, so made out
the report FYI. seems a false positive. sorry about cost your time to check.

> 
> Reinette