Re: [PATCH v2] futex: Use a keyed hash for global futex buckets

[Kyle Zeng <kylebot@openai.com>]

On Thu, Nov 05, 2026 at 09:04:47AM +0800, kernel test robot wrote:
> 
> Hello,
> 
> kernel test robot noticed a -6.0% regression of will-it-scale.per_thread_ops on:
> 
> 
> commit: c44a057178cbedbc04c63404258524975e87a64f ("[PATCH v2] futex: Use a keyed hash for global futex buckets")
> url: https://github.com/intel-lab-lkp/linux/commits/Kyle-Zeng/futex-Use-a-keyed-hash-for-global-futex-buckets/20261019-113334
> patch link: https://lore.kernel.org/all/20261019183334.29433-1-kylebot@openai.com/
> patch subject: [PATCH v2] futex: Use a keyed hash for global futex buckets
> 
> testcase: will-it-scale
> config: x86_64-rhel-9.4
> compiler: gcc-14
> test machine: 224 threads 2 sockets Intel(R) Xeon(R) Platinum 8480CTDX (Sapphire Rapids) with 512G memory
> parameters:
> 
>   nr_task: 100%
>   mode: thread
>   test: futex2
>   cpufreq_governor: performance
> 
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <yi1.lai@intel.com>
> | Closes: https://lore.kernel.org/oe-lkp/202611050816.9e42490c-lkp@intel.com
> 
> 
> Details are as below:
> -------------------------------------------------------------------------------------------------->
> 
> 
> The kernel config and materials to reproduce are available at:
> https://download.01.org/0day-ci/archive/20261105/202611050816.9e42490c-lkp@intel.com
> 
> =========================================================================================
> compiler/cpufreq_governor/kconfig/mode/nr_task/rootfs/tbox_group/test/testcase:
>   gcc-14/performance/x86_64-rhel-9.4/thread/100%/debian-13-x86_64-20250902.cgz/lkp-spr-2sp5/futex2/will-it-scale
> 
> commit: 
>   0fcb05b723 ("Merge tag 'libcrypto-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux")
>   c44a057178 ("[PATCH v2] futex: Use a keyed hash for global futex buckets")
> 
> 0fcb05b72344f408 c44a057178cbedbc04c63404258
> ---------------- --------------------------- 
>          %stddev     %change         %stddev
>              \          |                \  
>  7.026e+08            -6.0%  6.607e+08        will-it-scale.224.threads
>    3136755            -6.0%    2949754        will-it-scale.per_thread_ops
>  7.026e+08            -6.0%  6.607e+08        will-it-scale.workload
> 
> 
> Disclaimer:
> Results have been estimated based on internal Intel analysis and are provided
> for informational purposes only. Any difference in system hardware or software
> design or configuration may affect actual performance.
> 
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
> 
> 

I wonder what is the best way to run this above regression test and what
will be an acceptable threshold for the patch to be merged.
I'd like to iterate on the patch, fixing the issue while avoiding the
the performance regression.

Best,
Kyle