From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932081AbeCIObS (ORCPT ); Fri, 9 Mar 2018 09:31:18 -0500 Received: from mail-it0-f66.google.com ([209.85.214.66]:33193 "EHLO mail-it0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751068AbeCIObR (ORCPT ); Fri, 9 Mar 2018 09:31:17 -0500 X-Google-Smtp-Source: AG47ELsO0tcGYOhX7Y6sx4Dduz5maQE5OQ8kyL39BQuBaE8OWzQzuSMFlT2HLqTVIvLwlVL+ByaAvA== From: Vince Weaver X-Google-Original-From: Vince Weaver Date: Fri, 9 Mar 2018 09:31:11 -0500 (EST) X-X-Sender: vince@macbook-air To: kan.liang@linux.intel.com, vincent.weaver@maine.edu, linux-kernel@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org, eranian@google.com, acme@redhat.com, hpa@zytor.com, alexander.shishkin@linux.intel.com, mingo@kernel.org, jolsa@redhat.com cc: linux-tip-commits@vger.kernel.org Subject: Re: [tip:perf/core] perf/x86/intel: Disable userspace RDPMC usage for large PEBS In-Reply-To: Message-ID: References: <1518474035-21006-6-git-send-email-kan.liang@linux.intel.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 9 Mar 2018, tip-bot for Kan Liang wrote: > Commit-ID: 1af22eba248efe2de25658041a80a3d40fb3e92e > Gitweb: https://git.kernel.org/tip/1af22eba248efe2de25658041a80a3d40fb3e92e > Author: Kan Liang > AuthorDate: Mon, 12 Feb 2018 14:20:35 -0800 > Committer: Ingo Molnar > CommitDate: Fri, 9 Mar 2018 08:22:23 +0100 > > perf/x86/intel: Disable userspace RDPMC usage for large PEBS > So this whole commit log is about disabling RDPMC usage for "large PEBS" but the actual change disables RDPMC if "PERF_X86_EVENT_FREERUNNING" Either the commit log is really misleading, or else a poor name was chosen for this feature. Vince > Userspace RDPMC cannot possibly work for large PEBS, which was introduced in: > > b8241d20699e ("perf/x86/intel: Implement batched PEBS interrupt handling (large PEBS interrupt threshold)") > > When the PEBS interrupt threshold is larger than one, there is no way > to get exact auto-reload times and value for userspace RDPMC. Disable > the userspace RDPMC usage when large PEBS is enabled. > > The only exception is when the PEBS interrupt threshold is 1, in which > case user-space RDPMC works well even with auto-reload events. > > Signed-off-by: Kan Liang > Signed-off-by: Peter Zijlstra (Intel) > Cc: Alexander Shishkin > Cc: Arnaldo Carvalho de Melo > Cc: Jiri Olsa > Cc: Linus Torvalds > Cc: Peter Zijlstra > Cc: Stephane Eranian > Cc: Thomas Gleixner > Cc: Vince Weaver > Cc: acme@kernel.org > Fixes: b8241d20699e ("perf/x86/intel: Implement batched PEBS interrupt handling (large PEBS interrupt threshold)") > Link: http://lkml.kernel.org/r/1518474035-21006-6-git-send-email-kan.liang@linux.intel.com > Signed-off-by: Ingo Molnar > --- > arch/x86/events/core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c > index 00a6251981d2..9c86e10f1196 100644 > --- a/arch/x86/events/core.c > +++ b/arch/x86/events/core.c > @@ -2117,7 +2117,8 @@ static int x86_pmu_event_init(struct perf_event *event) > event->destroy(event); > } > > - if (READ_ONCE(x86_pmu.attr_rdpmc)) > + if (READ_ONCE(x86_pmu.attr_rdpmc) && > + !(event->hw.flags & PERF_X86_EVENT_FREERUNNING)) > event->hw.flags |= PERF_X86_EVENT_RDPMC_ALLOWED; > > return err; >