Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753397AbcLFPdj (ORCPT ); Tue, 6 Dec 2016 10:33:39 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:58557 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751576AbcLFPdi (ORCPT ); Tue, 6 Dec 2016 10:33:38 -0500 Date: Tue, 6 Dec 2016 16:32:22 +0100 From: Peter Zijlstra To: "Liang, Kan" Cc: "mingo@redhat.com" , "acme@kernel.org" , "linux-kernel@vger.kernel.org" , "alexander.shishkin@linux.intel.com" , "tglx@linutronix.de" , "namhyung@kernel.org" , "jolsa@kernel.org" , "Hunter, Adrian" , "wangnan0@huawei.com" , "mark.rutland@arm.com" , "andi@firstfloor.org" Subject: Re: [PATCH V2 03/13] perf/x86: output sampling overhead Message-ID: <20161206153222.GB3061@worktop.programming.kicks-ass.net> References: <1480713561-6617-1-git-send-email-kan.liang@intel.com> <1480713561-6617-4-git-send-email-kan.liang@intel.com> <20161206112013.GJ3124@twins.programming.kicks-ass.net> <37D7C6CF3E00A74B8858931C1DB2F07750CA9EAE@SHSMSX103.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <37D7C6CF3E00A74B8858931C1DB2F07750CA9EAE@SHSMSX103.ccr.corp.intel.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1584 Lines: 45 On Tue, Dec 06, 2016 at 03:02:20PM +0000, Liang, Kan wrote: > > > > On Fri, Dec 02, 2016 at 04:19:11PM -0500, kan.liang@intel.com wrote: > > > From: Kan Liang > > > > > > On x86, NMI handler is the most important part which brings overhead > > > for sampling. Adding a pmu specific overhead type > > > PERF_PMU_SAMPLE_OVERHEAD for it. > > > > > > For other architectures which may don't have NMI, the overhead type > > > can be reused. > > > > > > Signed-off-by: Kan Liang > > > --- > > > arch/x86/events/core.c | 17 ++++++++++++++++- > > > arch/x86/events/perf_event.h | 2 ++ > > > include/uapi/linux/perf_event.h | 1 + > > > 3 files changed, 19 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index > > > 9d4bf3a..de40f96 100644 > > > --- a/arch/x86/events/core.c > > > +++ b/arch/x86/events/core.c > > > @@ -1397,6 +1397,9 @@ static void x86_pmu_del(struct perf_event > > > *event, int flags) > > > > > > perf_event_update_userpage(event); > > > > > > + if ((flags & PERF_EF_LOG) && cpuc->nmi_overhead.nr) > > > + perf_log_overhead(event, PERF_PMU_SAMPLE_OVERHEAD, > > > +&cpuc->nmi_overhead); > > > + > > > do_del: > > > if (x86_pmu.del) { > > > /* > > > > That's not at all mentioned in the changelog, and it clearly isn't > > nmi_overhead. > > Here it only records the overhead, not calculate. It doesn't record anything, it generates the output. And it doesn't explain why that needs to be in pmu::del(), in general that's a horrible thing to do.