From patchwork Mon Nov 13 01:15:39 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Rafael J. Wysocki" X-Patchwork-Id: 10055039 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 30E2760586 for ; Mon, 13 Nov 2017 01:15:55 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 191C92918A for ; Mon, 13 Nov 2017 01:15:55 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 0CA1D291E4; Mon, 13 Nov 2017 01:15:55 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id F2BCA2918A for ; Mon, 13 Nov 2017 01:15:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751061AbdKMBPw (ORCPT ); Sun, 12 Nov 2017 20:15:52 -0500 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:62958 "EHLO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750954AbdKMBPv (ORCPT ); Sun, 12 Nov 2017 20:15:51 -0500 Received: from 79.184.254.73.ipv4.supernova.orange.pl (79.184.254.73) (HELO aspire.rjw.lan) by serwer1319399.home.pl (79.96.170.134) with SMTP (IdeaSmtpServer 0.82) id b9bf8e12219ece74; Mon, 13 Nov 2017 02:15:49 +0100 From: "Rafael J. Wysocki" To: x86@kernel.org Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Linus Torvalds , LKML , Linux PM , Len Brown , WANG Chao Subject: [PATCH] x86 / CPU: Avoid unnecessary IPIs in arch_freq_get_on_cpu() Date: Mon, 13 Nov 2017 02:15:39 +0100 Message-ID: <1830825.NTYOMyctnU@aspire.rjw.lan> MIME-Version: 1.0 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Rafael J. Wysocki Even though aperfmperf_snapshot_khz() caches the samples.khz value to return if called again in a sufficiently short time, its caller, arch_freq_get_on_cpu(), still uses smp_call_function_single() to run it which may allow user space to trigger an IPI storm by reading from the scaling_cur_freq cpufreq sysfs file in a tight loop. To avoid that, move the decision on whether or not to return the cached samples.khz value to arch_freq_get_on_cpu(). Fixes: 4815d3c56d1e (cpufreq: x86: Make scaling_cur_freq behave more as expected) Signed-off-by: Rafael J. Wysocki Reviewed-by: WANG Chao --- This change was part of commit 941f5f0f6ef5 (x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo), but it was not the reason for the revert and it remains applicable. Thanks, Rafael --- arch/x86/kernel/cpu/Makefile | 2 +- arch/x86/kernel/cpu/aperfmperf.c | 11 +++++++---- arch/x86/kernel/cpu/proc.c | 4 +++- 3 files changed, 11 insertions(+), 6 deletions(-) Index: linux-pm/arch/x86/kernel/cpu/aperfmperf.c =================================================================== --- linux-pm.orig/arch/x86/kernel/cpu/aperfmperf.c +++ linux-pm/arch/x86/kernel/cpu/aperfmperf.c @@ -42,10 +42,6 @@ static void aperfmperf_snapshot_khz(void s64 time_delta = ktime_ms_delta(now, s->time); unsigned long flags; - /* Don't bother re-computing within the cache threshold time. */ - if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS) - return; - local_irq_save(flags); rdmsrl(MSR_IA32_APERF, aperf); rdmsrl(MSR_IA32_MPERF, mperf); @@ -74,6 +70,7 @@ static void aperfmperf_snapshot_khz(void unsigned int arch_freq_get_on_cpu(int cpu) { + s64 time_delta; unsigned int khz; if (!cpu_khz) @@ -82,6 +79,12 @@ unsigned int arch_freq_get_on_cpu(int cp if (!static_cpu_has(X86_FEATURE_APERFMPERF)) return 0; + /* Don't bother re-computing within the cache threshold time. */ + time_delta = ktime_ms_delta(ktime_get(), per_cpu(samples.time, cpu)); + khz = per_cpu(samples.khz, cpu); + if (khz && time_delta < APERFMPERF_CACHE_THRESHOLD_MS) + return khz; + smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1); khz = per_cpu(samples.khz, cpu); if (khz)