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

Byungchul Park
2024-05-22T14:16:03Z

On Wed, May 22, 2024 at 07:27:44PM +0900, Byungchul Park wrote:
> On Wed, May 22, 2024 at 03:38:04PM +0800, Huang, Ying wrote:
> > 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
>
> Yes, right. LUF(Lazy Unmap Flush) reduces TLB shootdown IPI further.
>
> > you have the number?
>
> You can find the number obtained from llama.cpp in this cover letter:
>
> https://lore.kernel.org/lkml/20240520021734.21527-1-byungchul@sk.com/
>
> If you meant the number from the same test above, XSBench + qemu, I will
> re-test with mm-unstable branch of mm tree and share the result shortly.

I retested the same test but based on a recent mm-unstable branch of mm
tree instead of v6.6-rc5. The result changed because of the different
base, from v6.6-rc5 to a recent mm-unstable branch of mm tree.

----------------------------------------------------
mm-unstable branch with 7e12beb8ca2a commit reverted
----------------------------------------------------

1) from output of XSBench

Threads: 14
Runtime: 1067.771 seconds
Lookups: 1,700,000,000
Lookups/s: 1,592,101

2) from /proc/vmstat

numa_hit 11502876
numa_miss 1130877
numa_foreign 1130877
numa_interleave 115
numa_local 5879006
numa_other 6754747
numa_pte_updates 19390661
numa_hint_faults 19319467
numa_hint_faults_local 0
numa_pages_migrated 5472749
pgmigrate_success 11593079
pgmigrate_fail 549666
compact_migrate_scanned 5408404
compact_daemon_migrate_scanned 5408404
pgdemote_kswapd 5610705
pgdemote_direct 0
nr_tlb_remote_flush 6200106
nr_tlb_remote_flush_received 84362539
nr_tlb_local_flush_all 39202
nr_tlb_local_flush_one 760046

3) from /proc/interrupts

TLB: 3812782 3840646 4806989 5235846 5127512 5048603
6012100 6022642 5088907 5212207 4076329 6014857
6017060 6014964 6009362 6018368 TLB shootdowns

4) from 'perf stat -a'

180449546 itlb.itlb_flush
768913454 tlb_flush.dtlb_thread
304745973 tlb_flush.stlb_any
119589742349 dTLB-load-misses
826525376 dTLB-store-misses
2950724801 iTLB-load-misses

---------------------------------------------------
mm-unstable branch with 7e12beb8ca2a commit applied
---------------------------------------------------

1) from output of XSBench

Threads: 14
Runtime: 1043.972 seconds
Lookups: 1,700,000,000
Lookups/s: 1,628,395

2) from /proc/vmstat

numa_hit 16865880
numa_miss 1129958
numa_foreign 1129958
numa_interleave 115
numa_local 8565072
numa_other 9430766
numa_pte_updates 19240583
numa_hint_faults 19239948
numa_hint_faults_local 0
numa_pages_migrated 8159078
pgmigrate_success 17000781
pgmigrate_fail 1410437
compact_migrate_scanned 5075605
compact_daemon_migrate_scanned 5075605
pgdemote_kswapd 8297460
pgdemote_direct 0
nr_tlb_remote_flush 1516807
nr_tlb_remote_flush_received 20938785
nr_tlb_local_flush_all 95801
nr_tlb_local_flush_one 740597

3) from /proc/interrupts

TLB: 927080 567584 840684 1484285 1495859 1408641
1496227 1493909 1359465 1227623 1265431 1496361
1392337 1489451 1495799 1494700 TLB shootdowns

4) from 'perf stat -a'

43564429 itlb.itlb_flush
272921880 tlb_flush.dtlb_thread
175495467 tlb_flush.stlb_any
119602211976 dTLB-load-misses
355190881 dTLB-store-misses
1539926469 iTLB-load-misses

---------------------------------------------------------
mm-unstable branch with 7e12beb8ca2a commit applied + LUF
---------------------------------------------------------

1) from output of XSBench

Threads: 14
Runtime: 1033.973 seconds
Lookups: 1,700,000,000
Lookups/s: 1,644,144

2) from /proc/vmstat

numa_hit 18617127
numa_miss 1075467
numa_foreign 1075467
numa_interleave 115
numa_local 9440134
numa_other 10252460
numa_pte_updates 19473883
numa_hint_faults 19470143
numa_hint_faults_local 0
numa_pages_migrated 8978959
pgmigrate_success 18675500
pgmigrate_fail 1577460
compact_migrate_scanned 5465414
compact_daemon_migrate_scanned 5465414
pgdemote_kswapd 9172431
pgdemote_direct 0
nr_tlb_remote_flush 85818
nr_tlb_remote_flush_received 1036316
nr_tlb_local_flush_all 34674
nr_tlb_local_flush_one 740870

3) from /proc/interrupts

TLB: 55328 31254 44449 72887 73407 73775
73353 73658 35802 68184 70998 73504
74072 64700 73718 73862 TLB shootdowns

4) from 'perf stat -a'

2054390 itlb.itlb_flush
150073902 tlb_flush.dtlb_thread
135630767 tlb_flush.stlb_any
117880065362 dTLB-load-misses
217521760 dTLB-store-misses
908338035 iTLB-load-misses

---

The result looks incredible. You can also see the result if you try to
test a workload triggering reclaim or migration with LUF.

Byungchul