From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752190AbeC0KKk (ORCPT ); Tue, 27 Mar 2018 06:10:40 -0400 Received: from terminus.zytor.com ([198.137.202.136]:42141 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750978AbeC0KKi (ORCPT ); Tue, 27 Mar 2018 06:10:38 -0400 Date: Tue, 27 Mar 2018 03:10:05 -0700 From: tip-bot for Eric Dumazet Message-ID: Cc: mingo@kernel.org, bp@alien8.de, eric.dumazet@gmail.com, linux-kernel@vger.kernel.org, hpa@zytor.com, tglx@linutronix.de, edumazet@google.com, hughd@google.com Reply-To: bp@alien8.de, mingo@kernel.org, eric.dumazet@gmail.com, hughd@google.com, linux-kernel@vger.kernel.org, hpa@zytor.com, edumazet@google.com, tglx@linutronix.de In-Reply-To: <20180323215818.127774-1-edumazet@google.com> References: <20180323215818.127774-1-edumazet@google.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/cleanups] x86/msr: Allow rdmsr_safe_on_cpu() to schedule Git-Commit-ID: 07cde313b2d21f728cec2836db7cdb55476f7a26 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 07cde313b2d21f728cec2836db7cdb55476f7a26 Gitweb: https://git.kernel.org/tip/07cde313b2d21f728cec2836db7cdb55476f7a26 Author: Eric Dumazet AuthorDate: Fri, 23 Mar 2018 14:58:17 -0700 Committer: Thomas Gleixner CommitDate: Tue, 27 Mar 2018 12:01:47 +0200 x86/msr: Allow rdmsr_safe_on_cpu() to schedule High latencies can be observed caused by a daemon periodically reading various MSR on all cpus. On KASAN enabled kernels ~10ms latencies can be observed simply reading one MSR. Even without KASAN, sending an IPI to a CPU, which is in a deep sleep state or in a long hard IRQ disabled section, waiting for the answer can consume hundreds of microseconds. All usage sites are in preemptible context, convert rdmsr_safe_on_cpu() to use a completion instead of busy polling. Overall daemon cpu usage was reduced by 35 %, and latencies caused by msr_read() disappeared. Signed-off-by: Eric Dumazet Signed-off-by: Thomas Gleixner Acked-by: Ingo Molnar Cc: Hugh Dickins Cc: Borislav Petkov Cc: Eric Dumazet Link: https://lkml.kernel.org/r/20180323215818.127774-1-edumazet@google.com --- arch/x86/lib/msr-smp.c | 32 ++++++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 8 deletions(-) diff --git a/arch/x86/lib/msr-smp.c b/arch/x86/lib/msr-smp.c index 693cce0be82d..761ba062afda 100644 --- a/arch/x86/lib/msr-smp.c +++ b/arch/x86/lib/msr-smp.c @@ -2,6 +2,7 @@ #include #include #include +#include #include static void __rdmsr_on_cpu(void *info) @@ -143,13 +144,19 @@ void wrmsr_on_cpus(const struct cpumask *mask, u32 msr_no, struct msr *msrs) } EXPORT_SYMBOL(wrmsr_on_cpus); +struct msr_info_completion { + struct msr_info msr; + struct completion done; +}; + /* These "safe" variants are slower and should be used when the target MSR may not actually exist. */ static void __rdmsr_safe_on_cpu(void *info) { - struct msr_info *rv = info; + struct msr_info_completion *rv = info; - rv->err = rdmsr_safe(rv->msr_no, &rv->reg.l, &rv->reg.h); + rv->msr.err = rdmsr_safe(rv->msr.msr_no, &rv->msr.reg.l, &rv->msr.reg.h); + complete(&rv->done); } static void __wrmsr_safe_on_cpu(void *info) @@ -161,17 +168,26 @@ static void __wrmsr_safe_on_cpu(void *info) int rdmsr_safe_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h) { + struct msr_info_completion rv; + call_single_data_t csd = { + .func = __rdmsr_safe_on_cpu, + .info = &rv, + }; int err; - struct msr_info rv; memset(&rv, 0, sizeof(rv)); + init_completion(&rv.done); + rv.msr.msr_no = msr_no; - rv.msr_no = msr_no; - err = smp_call_function_single(cpu, __rdmsr_safe_on_cpu, &rv, 1); - *l = rv.reg.l; - *h = rv.reg.h; + err = smp_call_function_single_async(cpu, &csd); + if (!err) { + wait_for_completion(&rv.done); + err = rv.msr.err; + } + *l = rv.msr.reg.l; + *h = rv.msr.reg.h; - return err ? err : rv.err; + return err; } EXPORT_SYMBOL(rdmsr_safe_on_cpu);