Re: [linus:master] [migrate_pages] 7e12beb8ca: vm-scalability.throughput -3.4% regression

[Huang, Ying]

"Liu, Yujie" <yujie.liu@xxxxxxxxx> writes:

> Hi Ying,
>
> On Mon, 2023-03-20 at 15:58 +0800, Huang, Ying wrote:
>> Hi, Yujie,
>>
>> kernel test robot <yujie.liu@xxxxxxxxx> writes:
>>
>> > Hello,
>> >
>> > FYI, we noticed a -3.4% regression of vm-scalability.throughput due to commit:
>> >
>> > commit: 7e12beb8ca2ac98b2ec42e0ea4b76cdc93b58654 ("migrate_pages: batch flushing TLB")
>> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>> >
>> > in testcase: vm-scalability
>> > on test machine: 96 threads 2 sockets Intel(R) Xeon(R) Platinum 8260L CPU @ 2.40GHz (Cascade Lake) with 128G memory
>> > with following parameters:
>> >
>> >         runtime: 300s
>> >         size: 512G
>> >         test: anon-cow-rand-mt
>> >         cpufreq_governor: performance
>> >
>> > test-description: The motivation behind this suite is to exercise functions and regions of the mm/ of the Linux kernel which are of interest to us.
>> > test-url: https://git.kernel.org/cgit/linux/kernel/git/wfg/vm-scalability.git/
>> >
>> >
>> > If you fix the issue, kindly add following tag
>> > > Reported-by: kernel test robot <yujie.liu@xxxxxxxxx>
>> > > Link: https://lore.kernel.org/oe-lkp/202303192325.ecbaf968-yujie.liu@xxxxxxxxx
>> >
>>
>> Thanks a lot for report!  Can you try whether the debug patch as
>> below can restore the regression?
>
> We've tested the patch and found the throughput score was partially
> restored from -3.6% to -1.4%, still with a slight performance drop.
> Please check the detailed data as follows:

Good!  Thanks for your detailed data!

>       0.09 ± 17%      +1.2        1.32 ±  7%      +0.4        0.45 ± 21%  perf-profile.children.cycles-pp.flush_tlb_func

It appears that we can reduce the unnecessary TLB flushing effectively
with the previous debug patch.  But the batched flush (full flush) is
still slower than the non-batched flush (flush one page).

Can you try the debug patch as below to check whether it can restore the
regression completely?  The new debug patch can be applied on top of the
previous debug patch.

Best Regards,
Huang, Ying

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