Messages in this thread | | | Date | Fri, 3 Jun 2005 18:30:10 +0200 | From | Andi Kleen <> | Subject | Re: [PATCH 3/4] new timeofday x86-64 arch specific changes (v. B1) |
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On Thu, Jun 02, 2005 at 07:50:33PM -0400, Parag Warudkar wrote: > On Thursday 02 June 2005 19:20, john stultz wrote: > > Could you see if the slowness you're feeling is correlated to the > > acpi_pm timesource? > > Speaking of which, the below code from arch/i386/timer_pm.c looks particularly > more taxing to me - 3 times read from ioport in a loop - not sure how many > time that executes. > > static inline u32 read_pmtmr(void) > { > u32 v1=0,v2=0,v3=0; > /* It has been reported that because of various broken > * chipsets (ICH4, PIIX4 and PIIX4E) where the ACPI PM time > * source is not latched, so you must read it multiple > * times to insure a safe value is read. > */ > do { > v1 = inl(pmtmr_ioport); > v2 = inl(pmtmr_ioport); > v3 = inl(pmtmr_ioport); > } while ((v1 > v2 && v1 < v3) || (v2 > v3 && v2 < v1) > || (v3 > v1 && v3 < v2)); > > Shouldn't that loop be limited to the broken chipsets - why would correct > people with correctly working chipsets carry this extra burden? (Or is it > insignificant?)
It is not insignificant and makes a lot of difference. On the x86-64 version of pmtimer I dropped it completely and so far nobody complained.
However I wonder why this new time system is using pmtimer by default at all. That is very broken because pmtimer is one of the slowest. I would suggest to duplicate the time source selection I have in the latest x86-64 (-rc5) time.c, that is optimal for all machines I know about (except that you might need to add cyclone and a non TSC fallback for i386)
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