git: e7a5b3bd0589 - main - Modify lock_delay() to increase the delay time after spinning

[Edward Tomasz Napierala]

The branch main has been updated by trasz:

URL: https://cgit.FreeBSD.org/src/commit/?id=e7a5b3bd058975ff3ffa346664690e54c641fc0f

commit e7a5b3bd058975ff3ffa346664690e54c641fc0f
Author:     Edward Tomasz Napierala <trasz at FreeBSD.org>
AuthorDate: 2021-02-25 18:48:50 +0000
Commit:     Edward Tomasz Napierala <trasz at FreeBSD.org>
CommitDate: 2021-02-25 18:55:26 +0000

    Modify lock_delay() to increase the delay time after spinning
    
    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
---
 sys/kern/subr_lock.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/sys/kern/subr_lock.c b/sys/kern/subr_lock.c
index a74f7e62db4a..8b08c61715b3 100644
--- a/sys/kern/subr_lock.c
+++ b/sys/kern/subr_lock.c
@@ -128,10 +128,6 @@ lock_delay(struct lock_delay_arg *la)
 	struct lock_delay_config *lc = la->config;
 	u_short i;
 
-	la->delay <<= 1;
-	if (__predict_false(la->delay > lc->max))
-		la->delay = lc->max;
-
 	for (i = la->delay; i > 0; i--)
 		cpu_spinwait();
 
@@ -141,6 +137,10 @@ lock_delay(struct lock_delay_arg *la)
 		if (restrict_starvation)
 			la->delay = lc->base;
 	}
+
+	la->delay <<= 1;
+	if (__predict_false(la->delay > lc->max))
+		la->delay = lc->max;
 }
 
 static u_int