Module Name: src
Committed By: rin
Date: Thu Jan 9 06:55:25 UTC 2025
Modified Files:
src/sys/arch/arm/cortex: gtmr.c
Log Message:
gtmr_delay: Put SPINLOCK_BACKOFF_HOOK in busy loop
It is expanded as a `yield` instruction for aarch64.
This slightly improves peak performance for some drivers on
MP environments, as tested by msaitoh@ (thanks!).
XXX
This is what OpenBSD does, while FreeBSD just busy-spins.
However, unfortunately, benefits from `yield` should be limited,
as we still read count register quite frequently.
For long-duration delays, Linux uses `wfit` and `wfet` insns if
provided, and falls back to `wfe` otherwise:
https://github.com/torvalds/linux/blob/master/arch/arm64/lib/delay.c#L26-L51
Event streams should be configured for this purpose.
To generate a diff of this commit:
cvs rdiff -u -r1.49 -r1.50 src/sys/arch/arm/cortex/gtmr.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/arm/cortex/gtmr.c
diff -u src/sys/arch/arm/cortex/gtmr.c:1.49 src/sys/arch/arm/cortex/gtmr.c:1.50
--- src/sys/arch/arm/cortex/gtmr.c:1.49 Thu Mar 3 06:26:28 2022
+++ src/sys/arch/arm/cortex/gtmr.c Thu Jan 9 06:55:25 2025
@@ -1,4 +1,4 @@
-/* $NetBSD: gtmr.c,v 1.49 2022/03/03 06:26:28 riastradh Exp $ */
+/* $NetBSD: gtmr.c,v 1.50 2025/01/09 06:55:25 rin Exp $ */
/*-
* Copyright (c) 2012 The NetBSD Foundation, Inc.
@@ -30,13 +30,14 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: gtmr.c,v 1.49 2022/03/03 06:26:28 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: gtmr.c,v 1.50 2025/01/09 06:55:25 rin Exp $");
#include <sys/param.h>
#include <sys/bus.h>
#include <sys/device.h>
#include <sys/intr.h>
#include <sys/kernel.h>
+#include <sys/lock.h>
#include <sys/percpu.h>
#include <sys/proc.h>
#include <sys/systm.h>
@@ -327,6 +328,7 @@ gtmr_delay(unsigned int n)
uint64_t last = gtmr_read_cntct(sc);
while (ticks > 0) {
+ SPINLOCK_BACKOFF_HOOK;
uint64_t curr = gtmr_read_cntct(sc);
if (curr >= last)
ticks -= (curr - last);
