Messages in this thread | | | Date | Sun, 10 Feb 2019 22:08:53 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] acpi_pm: Reduce PMTMR counter read contention |
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On Sat, 2 Feb 2019, Zhenzhong Duan wrote: > On 2019/1/31 22:26, Thomas Gleixner wrote:
> > > > I'm not against the change per se, but I really want to understand > > > > why we need all the complexity for something which should never be > > > > used in a real world deployment. > > > > > > > Hmm, it's a strong word of "never be used". Customers may happen to > > > use nohpet(sanity test?) and report bug to us. Sometimes they does > > > report a bug that reproduce with their customed config. There may > > > also be BIOS setting HPET disabled. > > > > And because the customer MAY do completely nonsensical things (and there > > are a lot more than the HPET) the kernel has to handle all of them? > > Ok, then. I don't have more suggestion to convince you.
You give up too fast :)
The point is, that we really want proper justifications for changes like this. Some 'may, could and more handwaving' simply does not cut it.
So if you can just describe a realistic scenario, which does not involve thoughtless flipping of BIOS options, then this becomes way more palatable.
> I just think of a simple fix as below. I think it will work for both hpet > and pmtmr. We will test it when the env is available.
> --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -1353,6 +1353,7 @@ static int change_clocksource(void *data) > > write_seqcount_end(&tk_core.seq); > raw_spin_unlock_irqrestore(&timekeeper_lock, flags); > + tick_clock_notify(); > > return 0; > } > @@ -1371,7 +1372,6 @@ int timekeeping_notify(struct clocksource *clock) > if (tk->tkr_mono.clock == clock) > return 0; > stop_machine(change_clocksource, clock, NULL); > - tick_clock_notify(); > return tk->tkr_mono.clock == clock ? 0 : -1; > }
This won't resolve the concurrency issues of HPET or PMTIMER in any way. Instead it breaks the careful orchestrated mechanism of clocksource change.
Thanks,
tglx
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