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Subjectkernel lock contention and scalability

To discover possible locking limitations to scalability, I have collected
locking statistics on a 2-way, 4-way, and 8-way performing as networked
database servers. I patched the [48]-way kernels with Kravetz's multiqueue
patch in the hope that mitigating runqueue_lock contention might better
reveal other lock contention.

In the attached document, I describe my test environment and excerpt
lockstat output to show the more contentious locks for a typical run on
each of my server configurations. I'm interested in comparing these data
to other lock contention data, so information regarding previous or ongoing
lock contention work would be appreciated. I'm aware of timer scalability
work ongoing at people.redhat.com/mingo/scalable-timers, but is anyone
working on reducing sem_ids contention?

--
Jonathan Lahr
IBM Linux Technology Center
Beaverton, Oregon
lahr@us.ibm.com
503-578-3385


server configuration:
hardware:
memory:
2-way: .5 Gb
4-way: 1 Gb
8-way: 1 Gb
cpus:
2-way: Pentium II, 300 MHz
[48]-way: Pentium III, 700 MHz
NICs: 100 Mbps ethernet (2)
software:
distribution: Redhat 7.0
kernel:
2-way: 2.4.0-test10 patched with lockmeter1.4.5-2.4.0
[48]-way: 2.4.0 patched with lockmeter1.4.5-2.4.0, 2.4.0.MQ1-sched.rt
database: postgresql-7.0.2-17
client: pgbench (distributed with postgresql)

lockstat excerpts:

2way:

SPINLOCKS HOLD WAIT
UTIL CON MEAN ( MAX ) MEAN ( MAX ) TOTAL NOWAIT SPIN REJECT NAME

4.04% 1.22% 50us( 3344us) 5.2us( 2014us) 36515 36068 447 0 kernel_flag
0.01% 3.47% 46us( 427us) 17us( 2014us) 144 139 5 0 do_coredump+0x24
0.00% 0.00% 960us( 960us) 0us 1 1 0 0 do_exit+0x94
0.00% 4.00% 2.0us( 4.2us) 75us( 1876us) 25 24 1 0 ext2_discard_prealloc+0x24
0.03% 0.70% 11us( 1048us) 1.3us( 682us) 1144 1136 8 0 ext2_get_block+0x50
1.78% 0.79% 455us( 3344us) 0.8us( 759us) 1766 1752 14 0 ext2_sync_file+0x28
0.62% 0.84% 12us( 1289us) 2.5us( 1717us) 23353 23157 196 0 real_lookup+0x68
1.46% 1.29% 186us( 2980us) 5.4us( 1824us) 3553 3507 46 0 schedule+0x490
0.01% 0.00% 456us( 596us) 0us 9 9 0 0 sync_old_buffers+0x20
0.01% 1.83% 9.4us( 84us) 0.7us( 92us) 328 322 6 0 sys_fcntl64+0x44
0.00% 3.87% 8.0us( 329us) 6.7us( 1011us) 155 149 6 0 sys_ioctl+0x48
0.02% 2.79% 1.9us( 805us) 19us( 1986us) 5483 5330 153 0 sys_lseek+0x70
0.00% 0.00% 22us( 22us) 0us 1 1 0 0 sys_sysctl+0x50
0.01% 3.23% 17us( 84us) 0.5us( 25us) 155 150 5 0 tty_read+0xbc
0.02% 2.35% 39us( 110us) 0.2us( 11us) 213 208 5 0 tty_write+0x1dc
0.07% 1.09% 168us( 1442us) 0.7us( 116us) 184 182 2 0 vfs_readdir+0x70
0.00% 0.00% 31us( 31us) 0us 1 1 0 0 vfs_statfs+0x54

24.38% 23.93% 15us( 218us) 4.3us( 111us) 744475 566289 178186 0 runqueue_lock
0.06% 15.97% 4.5us( 26us) 2.6us( 67us) 5592 4699 893 0 __wake_up+0xdc
0.00% 10.27% 0.4us( 1.3us) 1.5us( 60us) 146 131 15 0 deliver_signal+0x58
1.16% 8.59% 1.5us( 27us) 2.3us( 111us) 360313 329373 30940 0 process_timeout+0x14
0.00% 0.00% 0.6us( 0.6us) 0us 1 1 0 0 release+0x28
23.15% 38.78% 28us( 218us) 6.2us( 108us) 376292 230381 145911 0 schedule+0xe0
0.01% 45.34% 3.7us( 24us) 16us( 82us) 686 375 311 0 schedule+0x458
0.00% 0.00% 2.8us( 70us) 0us 89 89 0 0 schedule+0x504
0.01% 8.55% 3.0us( 18us) 1.9us( 68us) 1356 1240 116 0 wake_up_process+0x14

0.11% 4.97% 12us( 1113us) 1.0us( 1540us) 4041 3840 201 0 sem_ids+0x24
0.00% 1.32% 7.1us( 88us) 0.1us( 11us) 303 299 4 0 semctl_main+0x4c
0.06% 3.85% 11us( 281us) 0.5us( 81us) 2392 2300 92 0 sys_semop+0xe8
0.04% 7.80% 15us( 1113us) 2.2us( 1540us) 1346 1241 105 0 sys_semop+0x3c8

2.31% 6.86% 0.9us( 15us) 0.2us( 13us) 1102822 1027206 75616 0 timerlist_lock
1.07% 4.75% 1.3us( 11us) 0.1us( 8.8us) 365451 348102 17349 0 add_timer+0x14
0.00% 1.91% 0.3us( 4.2us) 0.1us( 4.5us) 3935 3860 75 0 del_timer+0x14
0.32% 5.71% 0.4us( 7.2us) 0.2us( 13us) 362967 342246 20721 0 del_timer_sync+0x2c
0.02% 1.47% 1.8us( 9.1us) 0.0us( 6.2us) 3942 3884 58 0 mod_timer+0x18
0.02% 0.09% 2.3us( 15us) 0.0us( 2.8us) 4514 4510 4 0 timer_bh+0xd0
0.89% 10.33% 1.1us( 7.6us) 0.3us( 8.2us) 362013 324604 37409 0 timer_bh+0x26c


4way:

SPINLOCKS HOLD WAIT
UTIL CON MEAN ( MAX ) MEAN ( MAX ) TOTAL NOWAIT SPIN REJECT NAME

0.18% 33.57% 6.0us( 89us) 3.2us( 114us) 97322 64653 32669 0 sem_ids+0x24
0.01% 15.07% 2.0us( 69us) 0.9us( 44us) 10551 8961 1590 0 semctl_main+0x50
0.00% 0.00% 1.3us( 3.7us) 0us 248 248 0 0 sys_semget+0xd0
0.07% 23.57% 4.1us( 86us) 3.1us( 105us) 54350 41537 12813 0 sys_semop+0xf0
0.10% 56.77% 10us( 89us) 4.2us( 114us) 32173 13907 18266 0 sys_semop+0x35c

0.13% 10.71% 0.4us( 3.6us) 0.2us( 18us) 1147726 1024826 122900 0 timerlist_lock
0.06% 9.85% 0.6us( 3.0us) 0.2us( 14us) 361475 325856 35619 0 add_timer+0x10
0.00% 0.19% 0.1us( 1.2us) 0.0us( 6.2us) 45152 45068 84 0 del_timer+0x14
0.03% 11.15% 0.3us( 2.4us) 0.2us( 18us) 341333 303277 38056 0 del_timer_sync+0x1c
0.01% 0.44% 0.5us( 3.6us) 0.0us( 7.2us) 46186 45981 205 0 mod_timer+0x18
0.01% 0.01% 0.5us( 2.9us) 0.0us( 1.2us) 32429 32425 4 0 timer_bh+0xcc
0.03% 15.24% 0.3us( 2.0us) 0.3us( 10us) 321151 272219 48932 0 timer_bh+0x254

0.00% 7.03% 0.2us( 2.3us) 0.2us( 20us) 6882 6398 484 0 add_wait_queue_exclusive+0x10
0.00% 50.00% 0.1us( 0.1us) 3.2us( 6.4us) 2 1 1 0 inet_wait_for_connect+0x104
0.07% 7.48% 0.8us( 13us) 0.2us( 13us) 294222 272202 22020 0 process_timeout+0x24
0.02% 10.56% 0.5us( 4.6us) 0us 114853 102721 0 12132 reschedule_idle+0x3a4
0.04% 15.82% 1.2us( 5.7us) 0us 101053 85069 0 15984 schedule+0x5a8
0.00% 12.64% 2.3us( 12us) 0.3us( 11us) 2461 2150 311 0 schedule+0xb44
0.00% 16.00% 1.6us( 3.0us) 0.5us( 3.5us) 50 42 8 0 schedule+0xb80
0.00% 10.36% 0.4us( 13us) 1.4us( 20us) 251 225 26 0 tcp_close+0x30
0.00% 5.24% 0.1us( 1.4us) 1.1us( 39us) 248 235 13 0 tcp_setsockopt+0x98


8way:

SPINLOCKS HOLD WAIT
UTIL CON MEAN ( MAX ) MEAN ( MAX ) TOTAL NOWAIT SPIN REJECT NAME

1.15% 9.78% 7.6us( 363us) 2.1us( 862us) 1560956 1408297 152659 0 io_request_lock
0.00% 45.45% 0.5us( 5.3us) 13us( 250us) 58066 31677 26389 0 __get_request_wait+0x70
0.72% 12.06% 28us( 363us) 2.5us( 696us) 266880 234706 32174 0 __make_request+0xfc
0.01% 21.74% 0.2us( 7.0us) 3.9us( 862us) 241846 189278 52568 0 blk_get_queue+0x14
0.25% 4.19% 8.2us( 87us) 0.8us( 303us) 310337 297332 13005 0 do_aic7xxx_isr+0x20
0.02% 3.39% 2.7us( 35us) 0.3us( 233us) 63155 61015 2140 0 generic_unplug_device+0x10
0.04% 6.39% 2.4us( 34us) 2.2us( 314us) 155168 145259 9909 0 scsi_dispatch_cmd+0x12c
0.03% 6.09% 1.9us( 12us) 1.2us( 285us) 155168 145725 9443 0 scsi_old_done+0x614
0.07% 0.06% 4.9us( 65us) 0.0us( 177us) 155168 155080 88 0 scsi_queue_next_request+0x18
0.02% 4.47% 1.2us( 11us) 0.9us( 349us) 155168 148225 6943 0 scsi_request_fn+0x338

0.28% 36.38% 7.1us( 973us) 4.6us( 987us) 405038 257673 147365 0 sem_ids+0x24
0.01% 19.36% 2.2us( 42us) 2.3us( 149us) 56047 45198 10849 0 semctl_main+0x50
0.00% 0.00% 1.9us( 98us) 0us 992 992 0 0 sys_semget+0xd0
0.12% 23.36% 5.6us( 232us) 3.4us( 987us) 214063 164056 50007 0 sys_semop+0xf0
0.15% 64.59% 12us( 973us) 7.5us( 973us) 133936 47427 86509 0 sys_semop+0x35c

0.54% 14.58% 0.6us( 12us) 0.5us( 78us) 8829923 7542237 1287686 0 timerlist_lock
0.21% 11.40% 0.8us( 12us) 0.4us( 78us) 2856951 2531286 325665 0 add_timer+0x10
0.00% 0.82% 0.1us( 8.1us) 0.0us( 28us) 158853 157543 1310 0 del_timer+0x14
0.12% 15.81% 0.4us( 7.8us) 0.5us( 76us) 2787756 2347125 440631 0 del_timer_sync+0x1c
0.02% 1.19% 0.9us( 9.6us) 0.0us( 28us) 183111 180931 2180 0 mod_timer+0x18
0.02% 0.08% 1.6us( 9.1us) 0.0us( 5.5us) 102552 102466 86 0 timer_bh+0xcc
0.18% 18.89% 0.7us( 8.0us) 0.5us( 42us) 2740700 2222886 517814 0 timer_bh+0x254

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