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.
