Messages in this thread | | | Subject | Re: perf_events: questions about cpu_has_ht_siblings() and offcore support | From | Lin Ming <> | Date | Fri, 22 Apr 2011 23:30:19 +0800 |
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On Fri, 2011-04-22 at 23:05 +0800, Stephane Eranian wrote: > On Fri, Apr 22, 2011 at 5:03 PM, Lin Ming <ming.m.lin@intel.com> wrote: > > On Fri, 2011-04-22 at 22:41 +0800, Stephane Eranian wrote: > >> On Fri, Apr 22, 2011 at 4:31 PM, Lin Ming <ming.m.lin@intel.com> wrote: > >> > On Fri, 2011-04-22 at 21:46 +0800, Stephane Eranian wrote: > >> >> On Fri, Apr 22, 2011 at 3:26 PM, Lin Ming <ming.m.lin@intel.com> wrote: > >> >> > On Fri, 2011-04-22 at 20:59 +0800, Stephane Eranian wrote: > >> >> >> Lin, > >> >> >> > >> >> >> In arch/x86/include/asm/smp.h, you added: > >> >> >> > >> >> >> static inline bool cpu_has_ht_siblings(void) > >> >> >> { > >> >> >> bool has_siblings = false; > >> >> >> #ifdef CONFIG_SMP > >> >> >> has_siblings = cpu_has_ht && smp_num_siblings > 1; > >> >> >> #endif > >> >> >> return has_siblings; > >> >> >> } > >> >> >> > >> >> >> I am wondering about the goal of this function. > >> >> >> > >> >> >> Is it supposed to return whether or not HT is enabled? > >> >> >> > >> >> >> Ht enabled != HT supported > >> >> > > >> >> > It's used to check if HT is supported. > >> >> > > >> >> Ok, that makes more sense. > >> >> > >> >> > But unfortunately, we didn't find a way to check if HT is enabled. > >> >> > So I just check if HT is supported. > >> >> > > >> >> >> > >> >> >> +static inline int is_ht_enabled(void) > >> >> >> +{ > >> >> >> + bool has_ht = false; > >> >> >> +#ifdef CONFIG_SMP > >> >> >> + int w; > >> >> >> + w = cpumask_weight(cpu_sibling_mask(smp_processor_id())); > >> >> >> + has_ht = cpu_has_ht && w > 1; > >> >> >> +#endif > >> >> >> + return has_ht; > >> >> >> +} > >> >> >> > >> >> >> OTOH, you need some validation even in the case HT is off. No two events > >> >> >> scheduled together on the same PMU can have different values for the extra > >> > > >> > I got it now. > >> > > >> >> >> reg. Thus, the fact that cpu_has_ht_siblings() is imune to HT state helps here, > >> >> >> but then what's the point of it? > >> >> > > >> >> > The points is to avoid the percore resource allocations(which are used > >> >> > to sync between HTs) if HT is not supported. > >> >> > > >> >> But if you check x86_pmu.extra_regs, that should do it as well. > >> > > >> > I don't understand here. > >> > Did you mean we can avoid the percore resource allocations by just > >> > checking x86_pmu.extra_regs? How? > >> > >> Is you have not extra_regs, i.e., regs that are shared, then why would > >> you need the percore allocation? > > > > But "extra_regs" does not imply they are regs that are shared. > > It only means some events need to set extra registers to work. > > > Do you have example of such register that would not require the > extra mutual exclusion either between HT threads or between > events on the same PMU?
No.
I was thinking the case that "extra_regs" may be per-thread, instead of pef-core.
So if there are "extra_regs" or not does not connected directly with if locking is needed or not.
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