Messages in this thread | | | Date | Fri, 22 Apr 2011 15:46:09 +0200 | Subject | Re: perf_events: questions about cpu_has_ht_siblings() and offcore support | From | Stephane Eranian <> |
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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 >> 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.
Suppose HT is disabled and I do:
perf stat -e offcore_response_0:dmd_data_rd,offcore_response_0:dmnd_rfo ......
This should still not be allowed.
I think in this case, HT supported will cause your code to still allocate the per-core struct. There will be no matching of per-core structs in starting(). So I suspect things work. -- 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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