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Hello Nikolai Artemiev, build bot (Jenkins),
I'd like you to reexamine a change. Please visit
https://review.coreboot.org/c/flashrom/+/80808?usp=email
to look at the new patch set (#3).
The following approvals got outdated and were removed: Code-Review+2 by Nikolai Artemiev, Verified+1 by build bot (Jenkins)
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. The error is always in the positive direction (i.e., sleep longer than the requested delay, not shorter than the request).
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/08/80808/3