Messages in this thread Patch in this message | | | Date | Thu, 25 May 2023 12:03:16 +0800 | Subject | Re: [linus:master] [mm] f95bdb700b: stress-ng.ramfs.ops_per_sec -88.8% regression | From | Qi Zheng <> |
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On 2023/5/24 19:56, Qi Zheng wrote: > > > On 2023/5/24 19:08, Qi Zheng wrote: > > [...] > >> >> Well, I just ran the following command and reproduced the result: >> >> stress-ng --timeout 60 --times --verify --metrics-brief --ramfs 9 & >> >> 1) with commit 42c9db3970483: >> >> stress-ng: info: [11023] setting to a 60 second run per stressor >> stress-ng: info: [11023] dispatching hogs: 9 ramfs >> stress-ng: info: [11023] stressor bogo ops real time usr time >> sys time bogo ops/s bogo ops/s >> stress-ng: info: [11023] (secs) (secs) >> (secs) (real time) (usr+sys time) >> stress-ng: info: [11023] ramfs 774966 60.00 10.18 >> 169.45 12915.89 4314.26 >> stress-ng: info: [11023] for a 60.00s run time: >> stress-ng: info: [11023] 1920.11s available CPU time >> stress-ng: info: [11023] 10.18s user time ( 0.53%) >> stress-ng: info: [11023] 169.44s system time ( 8.82%) >> stress-ng: info: [11023] 179.62s total time ( 9.35%) >> stress-ng: info: [11023] load average: 8.99 2.69 0.93 >> stress-ng: info: [11023] successful run completed in 60.00s (1 min, >> 0.00 secs) >> >> 2) with commit f95bdb700bc6b: >> >> stress-ng: info: [37676] dispatching hogs: 9 ramfs >> stress-ng: info: [37676] stressor bogo ops real time usr time >> sys time bogo ops/s bogo ops/s >> stress-ng: info: [37676] (secs) (secs) >> (secs) (real time) (usr+sys time) >> stress-ng: info: [37676] ramfs 168673 60.00 1.61 >> 39.66 2811.08 4087.47 >> stress-ng: info: [37676] for a 60.10s run time: >> stress-ng: info: [37676] 1923.36s available CPU time >> stress-ng: info: [37676] 1.60s user time ( 0.08%) >> stress-ng: info: [37676] 39.66s system time ( 2.06%) >> stress-ng: info: [37676] 41.26s total time ( 2.15%) >> stress-ng: info: [37676] load average: 7.69 3.63 2.36 >> stress-ng: info: [37676] successful run completed in 60.10s (1 min, >> 0.10 secs) >> >> The bogo ops/s (real time) did drop significantly. >> >> And the memory reclaimation was not triggered in the whole process. so >> theoretically no one is in the read critical section of shrinker_srcu. >> >> Then I found that some stress-ng-ramfs processes were in >> TASK_UNINTERRUPTIBLE state for a long time: >> >> root 42313 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42314 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42315 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42316 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42317 7.8 0.0 69592 1812 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> root 42318 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42319 7.8 0.0 69592 1812 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> root 42320 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42321 7.8 0.0 69592 1812 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> root 42322 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42323 7.8 0.0 69592 1812 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> root 42324 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42325 7.8 0.0 69592 1812 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> root 42326 0.0 0.0 69592 2068 pts/0 S 19:00 0:00 >> stress-ng-ramfs [run] >> root 42327 7.9 0.0 69592 1812 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> root 42328 7.9 0.0 69592 1812 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> root 42329 7.9 0.0 69592 1812 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> root 42330 7.9 0.0 69592 1556 pts/0 D 19:00 0:02 >> stress-ng-ramfs [run] >> >> Their call stack is as follows: >> >> cat /proc/42330/stack >> >> [<0>] __synchronize_srcu.part.21+0x83/0xb0 >> [<0>] unregister_shrinker+0x85/0xb0 >> [<0>] deactivate_locked_super+0x27/0x70 >> [<0>] cleanup_mnt+0xb8/0x140 >> [<0>] task_work_run+0x65/0x90 >> [<0>] exit_to_user_mode_prepare+0x1ba/0x1c0 >> [<0>] syscall_exit_to_user_mode+0x1b/0x40 >> [<0>] do_syscall_64+0x44/0x80 >> [<0>] entry_SYSCALL_64_after_hwframe+0x63/0xcd >> >> + RCU folks, Is this result as expected? I would have thought that >> synchronize_srcu() should return quickly if no one is in the read >> critical section. :( >> > > With the following changes, ops/s can return to previous levels:
Or just set rcu_expedited to 1: echo 1 > /sys/kernel/rcu_expedited
> > diff --git a/mm/vmscan.c b/mm/vmscan.c > index db2ed6e08f67..90f541b07cd1 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -763,7 +763,7 @@ void unregister_shrinker(struct shrinker *shrinker) > debugfs_entry = shrinker_debugfs_remove(shrinker); > up_write(&shrinker_rwsem); > > - synchronize_srcu(&shrinker_srcu); > + synchronize_srcu_expedited(&shrinker_srcu); > > debugfs_remove_recursive(debugfs_entry); > > stress-ng: info: [13159] dispatching hogs: 9 ramfs > stress-ng: info: [13159] stressor bogo ops real time usr time > sys time bogo ops/s bogo ops/s > stress-ng: info: [13159] (secs) (secs) > (secs) (real time) (usr+sys time) > stress-ng: info: [13159] ramfs 710062 60.00 9.63 > 157.26 11834.18 4254.75 > stress-ng: info: [13159] for a 60.00s run time: > stress-ng: info: [13159] 1920.14s available CPU time > stress-ng: info: [13159] 9.62s user time ( 0.50%) > stress-ng: info: [13159] 157.26s system time ( 8.19%) > stress-ng: info: [13159] 166.88s total time ( 8.69%) > stress-ng: info: [13159] load average: 9.49 4.02 1.65 > stress-ng: info: [13159] successful run completed in 60.00s (1 min, > 0.00 secs) > > Can we make synchronize_srcu() call synchronize_srcu_expedited() when no > one is in the read critical section? > >> >
-- Thanks, Qi
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