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

Byungchul Park
2024-05-22T02:16:23Z

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

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Byungchul