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Modify lock_delay() to increase the delay time after spinning

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Modify lock_delay() to increase the delay time after spinning,
not before.  Previously we would spin at least twice instead of once.
In NetApp's benchmarks this fixes a performance regression compared
to FreeBSD 10, which called cpu_spinwait() directly.

Reviewed By:	mjg
Sponsored by:	NetApp, Inc.
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D27331
This commit is contained in:
Edward Tomasz Napierala 2021-02-25 18:48:50 +00:00
parent 22267215d6
commit e7a5b3bd05
1 changed files with 4 additions and 4 deletions
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8
sys/kern/subr_lock.c
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@ -128,10 +128,6 @@ lock_delay(struct lock_delay_arg *la)
struct lock_delay_config *lc = la->config; struct lock_delay_config *lc = la->config;
u_short i; u_short i;
la->delay <<= 1;
if (__predict_false(la->delay > lc->max))
la->delay = lc->max;
for (i = la->delay; i > 0; i--) for (i = la->delay; i > 0; i--)
cpu_spinwait(); cpu_spinwait();
@ -141,6 +137,10 @@ lock_delay(struct lock_delay_arg *la)
if (restrict_starvation) if (restrict_starvation)
la->delay = lc->base; la->delay = lc->base;
} }
la->delay <<= 1;
if (__predict_false(la->delay > lc->max))
la->delay = lc->max;
} }
static u_int static u_int