Messages in this thread | | | Subject | Re: gettimeofday order of magnitude slower with pmtimer, which is default | From | john stultz <> | Date | Tue, 21 Mar 2006 11:23:19 -0800 |
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On Tue, 2006-03-21 at 10:26 +0900, OGAWA Hirofumi wrote: > Con Kolivas <kernel@kolivas.org> writes: > > > On Tuesday 21 March 2006 01:50, Andreas Mohr wrote: > > > >> I think it's crazy to do a safe tripled readout (with *very* expensive > >> I/O!) of the PM timer unconditionally on *all* systems when only a > >> (albeit not that small) subset of systems is affected by buggy (un-latched) > >> PM timers. > >> I want to improve things there; I can see three ways to do it: > >> a) maintain a blacklist (or probably better a whitelist) of systems that > >> are (not) affected > >> b) detect long-time timer accuracy, then switch to fast readout if timer > >> is verified to be accurate (no white/blacklist needed this way) > >> c) give up on PM timer completely > >> > >> Any comments on which way and how this could/should be done? > > > > The pm timer is very fast when the timer is latched and that strange loop uses > > hardly any cpu time. The same can't be said about the unlatched timer case > > where absurd amounts of cpu seem the norm. You have a catch 22 situation if > > you depend on the accuracy of the pm timer only to end up wasting time trying > > to actually use that timer. [snip] > And the following is test of gettimeofday(). Probably, we need a patch. Umm.... > > 2.6.16 (pmtmr) > Simple gettimeofday: 3.6532 microseconds > Simple gettimeofday: 3.6502 microseconds > Simple gettimeofday: 3.6522 microseconds > Simple gettimeofday: 3.6486 microseconds > Simple gettimeofday: 3.6539 microseconds > > 2.6.16+patch (pmtmr) > Simple gettimeofday: 1.4582 microseconds > Simple gettimeofday: 1.4593 microseconds > Simple gettimeofday: 1.4671 microseconds > Simple gettimeofday: 1.4650 microseconds > > 2.6.16 (tsc) > Simple gettimeofday: 0.4037 microseconds > Simple gettimeofday: 0.4037 microseconds > Simple gettimeofday: 0.4040 microseconds > Simple gettimeofday: 0.4037 microseconds > Simple gettimeofday: 0.4038 microseconds > -- > OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> > > > Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
In my TOD rework I've dropped the triple read, figuring if a problem arose we could blacklist the specific box. This patch covers that, so it looks like a good idea to me.
I've not tested it myself, but if you feel good about it, please send it to Andrew.
thanks -john
Acked-by: John Stultz <johnstul@us.ibm.com>
> --- > > arch/i386/kernel/timers/timer_pm.c | 74 ++++++++++++++++++++++++++++++------- > 1 file changed, 60 insertions(+), 14 deletions(-) > > diff -puN arch/i386/kernel/timers/timer_pm.c~pm-kill-workaround arch/i386/kernel/timers/timer_pm.c > --- linux-2.6/arch/i386/kernel/timers/timer_pm.c~pm-kill-workaround 2006-03-21 04:20:27.000000000 +0900 > +++ linux-2.6-hirofumi/arch/i386/kernel/timers/timer_pm.c 2006-03-21 04:31:48.000000000 +0900 > @@ -15,6 +15,7 @@ > #include <linux/module.h> > #include <linux/device.h> > #include <linux/init.h> > +#include <linux/pci.h> > #include <asm/types.h> > #include <asm/timer.h> > #include <asm/smp.h> > @@ -35,6 +36,7 @@ > * in arch/i386/acpi/boot.c */ > u32 pmtmr_ioport = 0; > > +static int pmtmr_need_workaround __read_mostly = 1; > > /* value of the Power timer at last timer interrupt */ > static u32 offset_tick; > @@ -45,24 +47,68 @@ static seqlock_t monotonic_lock = SEQLOC > > #define ACPI_PM_MASK 0xFFFFFF /* limit it to 24 bits */ > > +#ifdef CONFIG_PCI > +/* > + * PIIX4 Errata: > + * > + * The power management timer may return improper result when read. > + * Although the timer value settles properly after incrementing, > + * while incrementing there is a 3 ns window every 69.8 ns where the > + * timer value is indeterminate (a 4.2% chance that the data will be > + * incorrect when read). As a result, the ACPI free running count up > + * timer specification is violated due to erroneous reads. > + */ > +static int __init pmtmr_bug_check(void) > +{ > + struct pci_dev *dev; > + int pmtmr_has_bug = 0; > + u8 rev; > + > + dev = pci_get_device(PCI_VENDOR_ID_INTEL, > + PCI_DEVICE_ID_INTEL_82371AB_3, NULL); > + if (dev) { > + pci_read_config_byte(dev, PCI_REVISION_ID, &rev); > + /* the bug has been fixed in PIIX4M */ > + if (rev < 3) > + pmtmr_has_bug = 1; > + pci_dev_put(dev); > + } > + > + if (pmtmr_has_bug) > + printk(KERN_INFO > + "*** Found PM-Timer Bug on this chip. For workarounds a bug, this timer\n" > + "*** source is slow. Use other timer source (clock=).\n"); > + else > + pmtmr_need_workaround = 0; > + > + return 0; > +} > +device_initcall(pmtmr_bug_check); > +#endif > + > /*helper function to safely read acpi pm timesource*/ > 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)); > + if (unlikely(pmtmr_need_workaround)) { > + u32 v1, v2, v3; > + > + /* 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)); > + > + /* mask the output to 24 bits */ > + return v2 & ACPI_PM_MASK; > + } > > - /* mask the output to 24 bits */ > - return v2 & ACPI_PM_MASK; > + return inl(pmtmr_ioport) & ACPI_PM_MASK; > } > > > _ > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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