Brian Norris has uploaded this change for review. ( https://review.coreboot.org/c/flashrom/+/80808?usp=email )
Change subject: udelay: Lower the sleep vs delay threshold ......................................................................
udelay: Lower the sleep vs delay threshold
By default, we busy-loop (a.k.a., "delay") for most delay values, and only allow sleeping for large delays. But busy-looping is expensive, as it wastes CPU cycles.
In a simple program that runs a bunch of samples of [1] over 1000 samples, I find that for 0.1 s (100000 us):
64x2 AMD CPU (CONFIG_HZ=250 / CONFIG_NO_HZ_FULL=y): min diff: 60 us max diff: 831 us mean diff: 135 us
4+2 Mediatek MT8183 CPU (CONFIG_HZ=1000 / CONFIG_NO_HZ_IDLE=y / sysctl kernel.timer_highres=1): min diff: 70 us max diff: 1556 us mean diff: 146 us
4+2 Mediatek MT8183 CPU (CONFIG_HZ=1000 / CONFIG_NO_HZ_IDLE=y / sysctl kernel.timer_highres=0): min diff: 94 us max diff: 7222 us mean diff: 1201 us
i.e., maximum 1.5% error, typically ~0.1% error with high resolution timers. Max 7% error, typical 1% error with low resolution timers.
This seems reasonable.
[1] Stripped / pseudocode:
clock_gettime(CLOCK_MONOTONIC, before); nanosleep({ .tv_nsec = usecs * 1000 }, NULL); clock_gettime(CLOCK_MONOTONIC, after); diff = abs((after - before) / 1000 - usecs));
Change-Id: Ifd4821c66c5564f7c975c08769a6742f645e9be0 Signed-off-by: Brian Norris briannorris@chromium.org --- M udelay.c 1 file changed, 2 insertions(+), 2 deletions(-)
git pull ssh://review.coreboot.org:29418/flashrom refs/changes/08/80808/1
diff --git a/udelay.c b/udelay.c index 0005d39..c42de25 100644 --- a/udelay.c +++ b/udelay.c @@ -220,8 +220,8 @@ /* Precise delay. */ void default_delay(unsigned int usecs) { - /* If the delay is >1 s, use internal_sleep because timing does not need to be so precise. */ - if (usecs > 1000000) { + /* If the delay is >0.1 s, use internal_sleep because timing does not need to be so precise. */ + if (usecs > 100000) { internal_sleep(usecs); } else if (use_clock_gettime) { clock_usec_delay(usecs);