Re: [PATCH v10 00/12] LUF(Lazy Unmap Flush) reducing tlb numbers over 90%

Huang, Ying
2024-05-22T07:40:00Z

Hi, Byungchul,

Byungchul Park <byungchul@sk.com> writes:

> On Mon, May 13, 2024 at 10:44:29AM +0900, Byungchul Park wrote:
>> On Sat, May 11, 2024 at 03:15:01PM +0800, Huang, Ying wrote:
>> > Byungchul Park <byungchul@sk.com> writes:
>> >
>> > > Hi everyone,
>> > >
>> > > While I'm working with a tiered memory system e.g. CXL memory, I have
>> > > been facing migration overhead esp. tlb shootdown on promotion or
>> > > demotion between different tiers. Yeah.. most tlb shootdowns on
>> > > migration through hinting fault can be avoided thanks to Huang Ying's
>> > > work, commit 4d4b6d66db ("mm,unmap: avoid flushing tlb in batch if PTE
>> > > is inaccessible"). See the following link for more information:
>> > >
>> > > https://lore.kernel.org/lkml/20231115025755.GA29979@system.software.com/
>> >
>> > And, I still have interest of the performance impact of commit
>> > 7e12beb8ca2a ("migrate_pages: batch flushing TLB"). In the email above,
>> > you said that the performance of v6.5-rc5 + 7e12beb8ca2a reverted has
>> > better performance than v6.5-rc5. Can you provide more details? For
>> > example, the number of TLB flushing IPI for two kernels?
>>
>> Okay. I will test and share the result with what you asked me now once
>> I get available for the test.
>
> I should admit that the test using qemu is so unstable. While using
> qemu for the test, kernel with 7e12beb8ca2a applied gave better results
> sometimes and worse ones sometimes. I should've used a bare metal from
> the beginning. Sorry for making you confused with the unstable result.
>
> Since I thought you asked me for the test with the same environment in
> the link above, I used qemu to reproduce the similar result but changed
> the number of threads for the test from 16 to 14 to get rid of noise
> that might be introduced by other than the intended test just in case.
>
> As expected, the stats are better with your work:
>
> ------------------------------------------
> v6.6-rc5 with 7e12beb8ca2a commit reverted
> ------------------------------------------
>
> 1) from output of XSBench
>
> Threads: 14
> Runtime: 1127.043 seconds
> Lookups: 1,700,000,000
> Lookups/s: 1,508,371
>
> 2) from /proc/vmstat
>
> numa_hit 15580171
> numa_miss 1034233
> numa_foreign 1034233
> numa_interleave 773
> numa_local 7927442
> numa_other 8686962
> numa_pte_updates 24068923
> numa_hint_faults 24061125
> numa_hint_faults_local 0
> numa_pages_migrated 7426480
> pgmigrate_success 15407375
> pgmigrate_fail 1849
> compact_migrate_scanned 4445414
> compact_daemon_migrate_scanned 4445414
> pgdemote_kswapd 7651061
> pgdemote_direct 0
> nr_tlb_remote_flush 8080092
> nr_tlb_remote_flush_received 109915713
> nr_tlb_local_flush_all 53800
> nr_tlb_local_flush_one 770466
>
> 3) from /proc/interrupts
>
> TLB: 8022927 7840769 123588 7837008 7835967 7839837
> 7838332 7839886 7837610 7837221 7834524 407260
> 7430090 7835696 7839081 7712568 TLB shootdowns
>
> 4) from 'perf stat -a'
>
> 222371217 itlb.itlb_flush
> 919832520 tlb_flush.dtlb_thread
> 372223809 tlb_flush.stlb_any
> 120210808042 dTLB-load-misses
> 979352769 dTLB-store-misses
> 3650767665 iTLB-load-misses
>
> -----------------------------------------
> v6.6-rc5 with 7e12beb8ca2a commit applied
> -----------------------------------------
>
> 1) from output of XSBench
>
> Threads: 14
> Runtime: 1105.521 seconds
> Lookups: 1,700,000,000
> Lookups/s: 1,537,737
>
> 2) from /proc/vmstat
>
> numa_hit 24148399
> numa_miss 797483
> numa_foreign 797483
> numa_interleave 772
> numa_local 12214575
> numa_other 12731307
> numa_pte_updates 24250278
> numa_hint_faults 24199756
> numa_hint_faults_local 0
> numa_pages_migrated 11476195
> pgmigrate_success 23634639
> pgmigrate_fail 1391
> compact_migrate_scanned 3760803
> compact_daemon_migrate_scanned 3760803
> pgdemote_kswapd 11932217
> pgdemote_direct 0
> nr_tlb_remote_flush 2151945
> nr_tlb_remote_flush_received 29672808
> nr_tlb_local_flush_all 124006
> nr_tlb_local_flush_one 741165
>
> 3) from /proc/interrupts
>
> TLB: 2130784 2120142 2117571 844962 2071766 114675
> 2117258 2119596 2116816 1205446 2119176 2119209
> 2116792 2118763 2118773 2117762 TLB shootdowns
>
> 4) from 'perf stat -a'
>
> 60851902 itlb.itlb_flush
> 334068491 tlb_flush.dtlb_thread
> 223732916 tlb_flush.stlb_any
> 120207083382 dTLB-load-misses
> 446823059 dTLB-store-misses
> 1926669373 iTLB-load-misses
>

Thanks a lot for test results!

From your test results, the TLB shootdown IPI can be reduced effectively
with commit 7e12beb8ca2a. So that the benchmark score improved a
little.

And, your changes will reduce the TLB shootdown IPI further, right? Do
you have the number?

--
Best Regards,
Huang, Ying