From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B49A5C04AB6 for ; Tue, 28 May 2019 12:44:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8DD0420883 for ; Tue, 28 May 2019 12:44:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="d0ZmRbMZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727508AbfE1Mn4 (ORCPT ); Tue, 28 May 2019 08:43:56 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49718 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727239AbfE1Mn4 (ORCPT ); Tue, 28 May 2019 08:43:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=d1+i8FlqvZy+DZCyf6x+0+OU5pzU76eA12cyixRHZMw=; b=d0ZmRbMZ2FxnVIyiCx1WmtxZb ykmUwzb2v1f/D9dWvWix6OWElCYB7UAhbTgbY/f248GD00SyMm1UeaSVCp2BefOoIxbVXcjYOhpPb kGzdl2M0lT2Cgs012Ca1LCopXW//8EyG1tfwImOSAdmmw19G6OZH/YFR0rcu6BhehnnesYo/H7BvD tCzMzkOIyVaiMNiV7D6F1MwGC1h5uXD9RrddhosnRiWiglrS+X+IjOO5REaBOOk+yb/y92Nqw22rn a3SRPTqFAoXuZkvwBaeHJPcoBTmNfmZSKaMRmstp5dZy/usXi0jyzX2/n0+Xl09mbLonNqRGyWYEc gzzxJg96w==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hVbSI-0003Zr-Lp; Tue, 28 May 2019 12:43:50 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 663E4200A0444; Tue, 28 May 2019 14:43:49 +0200 (CEST) Date: Tue, 28 May 2019 14:43:49 +0200 From: Peter Zijlstra To: kan.liang@linux.intel.com Cc: acme@kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, jolsa@kernel.org, eranian@google.com, alexander.shishkin@linux.intel.com, ak@linux.intel.com Subject: Re: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics Message-ID: <20190528124349.GU2606@hirez.programming.kicks-ass.net> References: <20190521214055.31060-1-kan.liang@linux.intel.com> <20190521214055.31060-5-kan.liang@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190521214055.31060-5-kan.liang@linux.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 21, 2019 at 02:40:50PM -0700, kan.liang@linux.intel.com wrote: > The 8bit metrics ratio values lose precision when the measurement period > gets longer. > > To avoid this we always reset the metric value when reading, as we > already accumulate the count in the perf count value. > > For a long period read, low precision is acceptable. > For a short period read, the register will be reset often enough that it > is not a problem. > The PERF_METRICS may report wrong value if its delta was less than 1/255 > of SLOTS (Fixed counter 3). > > To avoid this, the PERF_METRICS and SLOTS registers have to be reset > simultaneously. The slots value has to be cached as well. That doesn't sound like it is NMI-safe. > RDPMC > ========= > The TopDown can be collected per thread/process. To use TopDown > through RDPMC in applications on Icelake, the metrics and slots values > have to be saved/restored during context switching. > > Add specific set_period() to specially handle the slots and metrics > event. Because, > - The initial value must be 0. > - Only need to restore the value in context switch. For other cases, > the counters have been cleared after read. So the above claims to explain RDPMC, but doesn't mention that magic value below at all. In fact, I don't see how the above relates to RDPMC at all. > @@ -2141,7 +2157,9 @@ static int x86_pmu_event_idx(struct perf_event *event) > if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) > return 0; > > - if (x86_pmu.num_counters_fixed && idx >= INTEL_PMC_IDX_FIXED) { > + if (is_metric_idx(idx)) > + idx = 1 << 29; I can't find this in the SDM RDPMC description. What does it return? > + else if (x86_pmu.num_counters_fixed && idx >= INTEL_PMC_IDX_FIXED) { > idx -= INTEL_PMC_IDX_FIXED; > idx |= 1 << 30; > }