From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932406AbeCLOIO (ORCPT ); Mon, 12 Mar 2018 10:08:14 -0400 Received: from mga03.intel.com ([134.134.136.65]:6517 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932203AbeCLOIN (ORCPT ); Mon, 12 Mar 2018 10:08:13 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.47,461,1515484800"; d="scan'208";a="23927061" Subject: Re: [tip:perf/core] perf/x86/intel: Disable userspace RDPMC usage for large PEBS To: Vince Weaver , Peter Zijlstra Cc: linux-kernel@vger.kernel.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, linux-tip-commits@vger.kernel.org References: <1518474035-21006-6-git-send-email-kan.liang@linux.intel.com> <20180309174218.GB4064@hirez.programming.kicks-ass.net> From: "Liang, Kan" Message-ID: Date: Mon, 12 Mar 2018 10:08:09 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/9/2018 2:10 PM, Vince Weaver wrote: > On Fri, 9 Mar 2018, Peter Zijlstra wrote: > >> On Fri, Mar 09, 2018 at 09:31:11AM -0500, Vince Weaver wrote: >>> 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. >> >> Its the same thing, and yes that might want renaming I suppose. > > I apologize for noticing these things so late in the game, but I haven't > had time to keep up with a full lkml feed recently so I only see these > things once I'm CC'd on them. > > So to summarize this: rdpmc is only disabled on a per-event basis, and > only if that event is doing multi-pebs sampling? > If the event can do multi-pebs sampling, the rdpmc will be disabled. Other events which cannot do multi-pebs will not be impacted. To enable multi-pebs sampling for event, it requires a fixed period. It doesn't support callgraph. For older platform (before SKL), it doesn't support time stamp. Thanks, Kan > If that's true, then I don't think I have an issue with this. > > We finally got rdpmc support in a released PAPI, and it is a massive > improvement when self-monitoring (even moreso if KPTI is enabled) so I was > just trying to make sure this wouldn't suddenly disable rdpmc out from > under us. > > Vince >