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lockprof: use IPI-injecetd fences to fix hangs on stat dump and reset

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The previously used quiesce_all_cpus walks all CPUs and waits until curthread
can run on them. Even on contemporary machines this becomes a significant
problem under load when it can literally take minutes for the operation to
complete. With the patch the stall is normally less than 1 second.

Reviewed by:	kib, jeff (previous version)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D21740
This commit is contained in:
Mateusz Guzik 2019-11-30 17:24:42 +00:00
parent 5032fe17a2
commit 3ac2ac2e08
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=355231
1 changed files with 24 additions and 2 deletions
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26
sys/kern/subr_lock.c
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@ -324,7 +324,13 @@ lock_prof_reset(void)
atomic_store_rel_int(&lock_prof_resetting, 1);
enabled = lock_prof_enable;
lock_prof_enable = 0;
quiesce_all_cpus("profreset", 0);
/*
* This both publishes lock_prof_enable as disabled and makes sure
* everyone else reads it if they are not far enough. We wait for the
* rest down below.
*/
cpus_fence_seq_cst();
quiesce_all_critical();
/*
* Some objects may have migrated between CPUs. Clear all links
* before we zero the structures. Some items may still be linked
@ -343,6 +349,9 @@ lock_prof_reset(void)
lock_prof_init_type(&lpc->lpc_types[0]);
lock_prof_init_type(&lpc->lpc_types[1]);
}
/*
* Paired with the fence from cpus_fence_seq_cst()
*/
atomic_store_rel_int(&lock_prof_resetting, 0);
lock_prof_enable = enabled;
}
@ -433,12 +442,17 @@ dump_lock_prof_stats(SYSCTL_HANDLER_ARGS)
"max", "wait_max", "total", "wait_total", "count", "avg", "wait_avg", "cnt_hold", "cnt_lock", "name");
enabled = lock_prof_enable;
lock_prof_enable = 0;
quiesce_all_cpus("profstat", 0);
/*
* See the comment in lock_prof_reset
*/
cpus_fence_seq_cst();
quiesce_all_critical();
t = ticks;
CPU_FOREACH(cpu) {
lock_prof_type_stats(&LP_CPU(cpu)->lpc_types[0], sb, 0, t);
lock_prof_type_stats(&LP_CPU(cpu)->lpc_types[1], sb, 1, t);
}
atomic_thread_fence_rel();
lock_prof_enable = enabled;
error = sbuf_finish(sb);
@ -591,6 +605,10 @@ lock_profile_obtain_lock_success(struct lock_object *lo, int contested,
else
l->lpo_waittime = 0;
out:
/*
* Paired with cpus_fence_seq_cst().
*/
atomic_thread_fence_rel();
critical_exit();
}
@ -677,6 +695,10 @@ lock_profile_release_lock(struct lock_object *lo)
type = &LP_CPU_SELF->lpc_types[spin];
LIST_INSERT_HEAD(&type->lpt_lpoalloc, l, lpo_link);
out:
/*
* Paired with cpus_fence_seq_cst().
*/
atomic_thread_fence_rel();
critical_exit();
}