Hi Rafael, Len, On 18-Nov-24 12:03 PM, Rafael J. Wysocki wrote: > On Sat, Nov 16, 2024 at 12:11 AM Len Brown <lenb@xxxxxxxxxx> wrote: >> >> From: Len Brown <len.brown@xxxxxxxxx> >> >> Replace msleep() with usleep_range() in acpi_os_sleep(). >> >> This has a significant user-visible performance benefit >> on some ACPI flows on some systems. eg. Kernel resume >> time of a Dell XPS-13-9300 drops from 1943ms to 1127ms (42%). > > Sure. > > And the argument seems to be that it is better to always use more > resources in a given path (ACPI sleep in this particular case) than to > be somewhat inaccurate which is visible in some cases. > > This would mean that hrtimers should always be used everywhere, but they aren't. > > While I have nothing against addressing the short sleeps issue where > the msleep() inaccuracy is too large, I don't see why this requires > using a hrtimer with no slack in all cases. > > The argument seems to be that the short sleeps case is hard to > distinguish from the other cases, but I'm not sure about this. > > Also, something like this might work, but for some reason you don't > want to do it: > > if (ms >= 12 * MSEC_PER_SEC / HZ) { > msleep(ms); > } else { > u64 us = ms * USEC_PER_MSEC; > > usleep_range(us, us / 8); > } FWIW I was thinking the same thing, that it would be good to still use msleep when the sleep is > (MSEC_PER_SEC / HZ), not sure why you added the 12 there ? Surely something like a sleep longer then 3 timerticks (I know we have NOHZ but still) would already be long enough to not worry about msleep slack ? And I assume the usleep_range(us, us / 8); is a typo ? Ma can never be less then max, maybe you meant: usleep_range(us, us + 8) ? OTOH it is not like we will hit these ACPI acpi_os_sleep() calls multiple times per second all the time. On a normal idle system I expect there to not be that many calls (could still be a few from ACPI managed devices going into + out of runtime-pm regularly). And if don't hit acpi_os_sleep() calls multiple times per second then the chances of time coalescing are not that big anyways. Still I think that finding something middle ground between always sleeping the exact min time and the old msleep() call, as Rafael is proposing, would be good IMHO. Regards, Hans > >> usleep_range(min, min) is used because there is scant >> opportunity for timer coalescing during ACPI flows >> related to system suspend, resume (or initialization). >> >> ie. During these flows usleep_range(min, max) is observed to >> be effectvely be the same as usleep_range(max, max). >> >> Similarly, msleep() for long sleeps is not considered because >> these flows almost never have opportunities to coalesce >> with other activity on jiffie boundaries, leaving no >> measurably benefit to rounding up to jiffie boundaries. >> >> Background: >> >> acpi_os_sleep() supports the ACPI AML Sleep(msec) operator, >> and it must not return before the requested number of msec. >> >> Until Linux-3.13, this contract was sometimes violated by using >> schedule_timeout_interruptible(j), which could return early. >> >> Since Linux-3.13, acpi_os_sleep() uses msleep(), >> which doesn't return early, but is still subject >> to long delays due to the low resolution of the jiffie clock. >> >> Linux-6.12 removed a stray jiffie from msleep: commit 4381b895f544 >> ("timers: Remove historical extra jiffie for timeout in msleep()") >> The 4ms savings is material for some durations, >> but msleep is still generally too course. eg msleep(5) >> on a 250HZ system still takes 11.9ms. >> >> System resume performance of a Dell XPS 13 9300: >> >> Linux-6.11: >> msleep HZ 250 2460 ms >> >> Linux-6.12: >> msleep HZ 250 1943 ms >> msleep HZ 1000 1233 ms >> usleep HZ 250 1127 ms >> usleep HZ 1000 1130 ms >> >> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=216263 >> Signed-off-by: Len Brown <len.brown@xxxxxxxxx> >> Suggested-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> >> Tested-by: Todd Brandt <todd.e.brandt@xxxxxxxxx> >> --- >> drivers/acpi/osl.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c >> index 70af3fbbebe5..daf87e33b8ea 100644 >> --- a/drivers/acpi/osl.c >> +++ b/drivers/acpi/osl.c >> @@ -607,7 +607,9 @@ acpi_status acpi_os_remove_interrupt_handler(u32 gsi, acpi_osd_handler handler) >> >> void acpi_os_sleep(u64 ms) >> { >> - msleep(ms); >> + u64 us = ms * USEC_PER_MSEC; >> + >> + usleep_range(us, us); >> } >> >> void acpi_os_stall(u32 us) >> -- >> 2.43.0 >> >