| Message ID | 20110309143842.6c22845e@kryten (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
* Anton Blanchard <anton@samba.org> wrote: > > Events on POWER7 can roll back if a speculative event doesn't > eventually complete. Unfortunately in some rare cases they will > raise a performance monitor exception. We need to catch this to > ensure we reset the PMC. In all cases the PMC will be 256 or less > cycles from overflow. > > Signed-off-by: Anton Blanchard <anton@samba.org> > Cc: stable@kernel.org > --- > > I would prefer not to add the PVR check, but I think we want to limit > this workaround to POWER7. Would a cpu feature be preferable? There was no objection from the PowerPC folks so i'll send this fix Linuswards, ok? Thanks, Ingo
On Wed, 2011-03-16 at 13:50 +0100, Ingo Molnar wrote: > * Anton Blanchard <anton@samba.org> wrote: > > > > > Events on POWER7 can roll back if a speculative event doesn't > > eventually complete. Unfortunately in some rare cases they will > > raise a performance monitor exception. We need to catch this to > > ensure we reset the PMC. In all cases the PMC will be 256 or less > > cycles from overflow. > > > > Signed-off-by: Anton Blanchard <anton@samba.org> > > Cc: stable@kernel.org > > --- > > > > I would prefer not to add the PVR check, but I think we want to limit > > this workaround to POWER7. Would a cpu feature be preferable? > > There was no objection from the PowerPC folks so i'll send this fix Linuswards, ok? Ah yes. Ack. Cheers, Ben.
Index: linux-2.6/arch/powerpc/kernel/perf_event.c =================================================================== --- linux-2.6.orig/arch/powerpc/kernel/perf_event.c 2011-03-08 20:11:38.029800971 +1100 +++ linux-2.6/arch/powerpc/kernel/perf_event.c 2011-03-09 14:19:18.756143799 +1100 @@ -1269,6 +1269,28 @@ unsigned long perf_instruction_pointer(s return ip; } +static bool pmc_overflow(unsigned long val) +{ + if ((int)val < 0) + return true; + + /* + * Events on POWER7 can roll back if a speculative event doesn't + * eventually complete. Unfortunately in some rare cases they will + * raise a performance monitor exception. We need to catch this to + * ensure we reset the PMC. In all cases the PMC will be 256 or less + * cycles from overflow. + * + * We only do this if the first pass fails to find any overflowing + * PMCs because a user might set a period of less than 256 and we + * don't want to mistakenly reset them. + */ + if (__is_processor(PV_POWER7) && ((0x80000000 - val) <= 256)) + return true; + + return false; +} + /* * Performance monitor interrupt stuff */ @@ -1316,7 +1338,7 @@ static void perf_event_interrupt(struct if (is_limited_pmc(i + 1)) continue; val = read_pmc(i + 1); - if ((int)val < 0) + if (pmc_overflow(val)) write_pmc(i + 1, 0); } } Index: linux-2.6/arch/powerpc/include/asm/reg.h =================================================================== --- linux-2.6.orig/arch/powerpc/include/asm/reg.h 2011-03-08 20:11:38.019800609 +1100 +++ linux-2.6/arch/powerpc/include/asm/reg.h 2011-03-09 14:13:56.674461835 +1100 @@ -880,6 +880,7 @@ #define PV_970 0x0039 #define PV_POWER5 0x003A #define PV_POWER5p 0x003B +#define PV_POWER7 0x003F #define PV_970FX 0x003C #define PV_630 0x0040 #define PV_630p 0x0041
Events on POWER7 can roll back if a speculative event doesn't eventually complete. Unfortunately in some rare cases they will raise a performance monitor exception. We need to catch this to ensure we reset the PMC. In all cases the PMC will be 256 or less cycles from overflow. Signed-off-by: Anton Blanchard <anton@samba.org> Cc: stable@kernel.org --- I would prefer not to add the PVR check, but I think we want to limit this workaround to POWER7. Would a cpu feature be preferable?