From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753793Ab2B0Lji (ORCPT ); Mon, 27 Feb 2012 06:39:38 -0500 Received: from casper.infradead.org ([85.118.1.10]:59018 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752171Ab2B0Ljh convert rfc822-to-8bit (ORCPT ); Mon, 27 Feb 2012 06:39:37 -0500 Message-ID: <1330342762.11248.69.camel@twins> Subject: Re: [PATCH] perf_event use rdpmc rather than rdmsr when possible in kernel From: Peter Zijlstra To: Vince Weaver Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, Paul Mackerras , Arnaldo Carvalho de Melo , Stephane Eranian Date: Mon, 27 Feb 2012 12:39:22 +0100 In-Reply-To: References: Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-02-20 at 17:38 -0500, Vince Weaver wrote: > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > index 5adce10..5550047 100644 > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -85,7 +85,7 @@ u64 x86_perf_event_update(struct perf_event *event) > */ > again: > prev_raw_count = local64_read(&hwc->prev_count); > - rdmsrl(hwc->event_base, new_raw_count); > + new_raw_count=native_read_pmc(hwc->event_base_rdpmc); That really wants to be rdpmc(), bypassing paravirt like that isn't nice. > > if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, > new_raw_count) != prev_raw_count) > @@ -768,9 +768,11 @@ static inline void x86_assign_hw_event(struct perf_event *event, > } else if (hwc->idx >= X86_PMC_IDX_FIXED) { > hwc->config_base = MSR_ARCH_PERFMON_FIXED_CTR_CTRL; > hwc->event_base = MSR_ARCH_PERFMON_FIXED_CTR0 + (hwc->idx - X86_PMC_IDX_FIXED); > + hwc->event_base_rdpmc = (hwc->idx - X86_PMC_IDX_FIXED) | 1<<30; > } else { > hwc->config_base = x86_pmu_config_addr(hwc->idx); > hwc->event_base = x86_pmu_event_addr(hwc->idx); > + hwc->event_base_rdpmc = x86_pmu_addr_offset(hwc->idx); > } > } > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index abb2776..432ac69 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -562,6 +562,7 @@ struct hw_perf_event { > u64 last_tag; > unsigned long config_base; > unsigned long event_base; > + unsigned long event_base_rdpmc; We could make that unsigned int, the SDM explicitly states rdmsr/wrmsr/rdpmc take ECX (and ignore the upper 32bits RCX). > int idx; > int last_cpu; > struct hw_perf_event_extra extra_reg; But yeah, avoiding the extra variable will add a conditional and extra instructions to the rdpmc path.