From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755620Ab1DVObs (ORCPT ); Fri, 22 Apr 2011 10:31:48 -0400 Received: from mga09.intel.com ([134.134.136.24]:60173 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750986Ab1DVObq (ORCPT ); Fri, 22 Apr 2011 10:31:46 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.64,253,1301900400"; d="scan'208";a="737052382" Subject: Re: perf_events: questions about cpu_has_ht_siblings() and offcore support From: Lin Ming To: Stephane Eranian Cc: LKML , "mingo@elte.hu" , Peter Zijlstra , "Kleen, Andi" In-Reply-To: References: <1303478798.2461.11.camel@localhost> Content-Type: text/plain; charset="UTF-8" Date: Fri, 22 Apr 2011 22:31:42 +0800 Message-Id: <1303482702.2461.40.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.28.0 (2.28.0-2.fc12) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2011-04-22 at 21:46 +0800, Stephane Eranian wrote: > On Fri, Apr 22, 2011 at 3:26 PM, Lin Ming 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? > > 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. Ah, you are right. We have to always check extra_config even HT is disabled and/or supported. > > 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. This has no problem. If "no matching" found, then below if(...) statement won't be executed. intel_pmu_cpu_starting: for_each_cpu(i, topology_thread_cpumask(cpu)) { struct intel_percore *pc = per_cpu(cpu_hw_events, i).per_core; if (pc && pc->core_id == core_id) { kfree(cpuc->per_core); cpuc->per_core = pc; break; } } Or do you see other potential problem?