Hi,
I had just run the rwsem microbenchmark on a 1-socket 44-core Qualcomm
Amberwing (Centriq 2400) arm64 system. There were 18 writer and 18
reader threads running.
For the patched kernel, the results were:
Reader Writer
CS Load Locking Ops/Thread Locking Ops/Thread
------- ------------------ ------------------
1 18,800/103,894/223,371 496,362/695,560/1,034,278
10 28,503/ 68,834/154,348 425,708/791,553/1,469,845
50 7,997/ 28,278/102,327 431,577/897,064/1,898,146
100 31,628/ 52,555/ 89,431 432,844/580,496/ 910,290
1us sleep 15,625/ 16,071/ 16,535 42,339/ 44,866/ 46,189
Reader Writer
CS Load Slowpath Locking Ops Slowpath Locking Ops
------- -------------------- --------------------
1 1,296,904 11,196,177
10 1,125,334 13,242,082
50 284,342 14,960,882
100 916,305 9,652,818
1us sleep 289,177 807,584
All Writers Half Writers
CS Load Locking Ops/Thread Locking Ops/Thread % Change
------- ------------------ ------------------ --------
1 1,634,230 695,560 -57.4
10 1,658,228 791,553 -52.3
50 1,494,180 897,064 -40.0
100 1,089,364 580,496 -46.7
1us sleep 25,380 44,866 +76.8
It is obvious that for arm64, the writers are preferred under all
circumstances. One special thing about the results was that for the
all writers case, the number of slowpath calls were exceedingly small.
It was about 1000 or less which are significantly less than in x86-64
which was in the millions. Maybe it was due to the LL/SC architecture
that allows it to stay in the fast path as much as possible with
homogenous operation.
The corresponding results for the unpatched kernel were:
Reader Writer
CS Load Locking Ops/Thread Locking Ops/Thread
------- ------------------ ------------------
1 23,898/23,899/23,905 45,264/177,375/461,387
10 25,114/25,115/25,122 26,188/190,517/458,960
50 23,762/23,762/23,763 67,862/174,640/269,519
100 25,050/25,051/25,053 57,214/200,725/814,178
1us sleep 6/ 6/ 7 6/ 58,512/180,892
All Writers Half Writers
CS Load Locking Ops/Thread Locking Ops/Thread % Change
------- ------------------ ------------------ --------
1 1,687,691 177,375 -89.5
10 1,627,061 190,517 -88.3
50 1,469,431 174,640 -88.1
100 1,148,905 200,725 -82.5
1us sleep 29,865 58,512 +95.9
Cheers,
Longman
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