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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 28DD2C2D0E4 for ; Fri, 20 Nov 2020 19:35:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E5A5D22264 for ; Fri, 20 Nov 2020 19:35:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EF6HUnl7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728615AbgKTTfQ (ORCPT ); Fri, 20 Nov 2020 14:35:16 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55486 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728282AbgKTTfP (ORCPT ); Fri, 20 Nov 2020 14:35:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1605900913; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XGRdA1sp4aWVP0lf2aD801Gns5XZWzMzikpu+pfp5Qc=; b=EF6HUnl7j5W2mGZsevmPx2PrhPNyriq1uT9OTsTRHuVEHc5T8VeF5Eztn58TxFCLKlFrf1 X58Qvr4s4KLk6FKyYENmw/W7IofcQUCXssxdKCbD9+YzBF8h7+COHMVWBw5psBkZi8UdHz kqwXEQGflCPiQxCxlzVbYQ/Po7Njxwc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-95--7AyUIfzOem0R47IS3syZg-1; Fri, 20 Nov 2020 14:35:09 -0500 X-MC-Unique: -7AyUIfzOem0R47IS3syZg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B64C3100A652; Fri, 20 Nov 2020 19:35:05 +0000 (UTC) Received: from krava (unknown [10.40.192.134]) by smtp.corp.redhat.com (Postfix) with SMTP id 58A775C224; Fri, 20 Nov 2020 19:35:02 +0000 (UTC) Date: Fri, 20 Nov 2020 20:35:01 +0100 From: Jiri Olsa To: Ian Rogers Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Namhyung Kim , LKML , Andi Kleen , Jin Yao , John Garry , Paul Clarke , kajoljain , Stephane Eranian , Sandeep Dasgupta , linux-perf-users Subject: Re: [PATCH v2 5/5] perf metric: Don't compute unused events. Message-ID: <20201120193501.GO1475102@krava> References: <20201118050335.2347358-1-irogers@google.com> <20201118050335.2347358-6-irogers@google.com> <20201119205920.GM1475102@krava> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 19, 2020 at 01:37:15PM -0800, Ian Rogers wrote: > On Thu, Nov 19, 2020 at 12:59 PM Jiri Olsa wrote: > > > On Tue, Nov 17, 2020 at 09:03:35PM -0800, Ian Rogers wrote: > > > > SNIP > > > > > + ids__free($1.ids); > > > + ids__free($3.ids); > > > + } > > > + } else { > > > + $$.val = NAN; > > > + $$.ids = ids__union($1.ids, $3.ids); > > > + } > > > +} > > > +| expr '*' expr > > > +{ > > > + if (!compute_ids || (isfinite($1.val) && isfinite($3.val))) { > > > + $$.val = $1.val * $3.val; > > > + $$.ids = NULL; > > > + if (compute_ids) { > > > + ids__free($1.ids); > > > + ids__free($3.ids); thanks for the explanation below, really nice, one more question ;-) why do we need to call ids__free in here, for compute_ids and constants case in here it should be always NULL, no? > > > + } > > > + } else { > > > + $$.val = NAN; > > > + $$.ids = ids__union($1.ids, $3.ids); > > > + } > > > +} > > > +| expr '/' expr > > > +{ > > > + if (fpclassify($3.val) == FP_ZERO) { > > > + pr_debug("division by zero\n"); > > > + YYABORT; > > > + } else if (!compute_ids || (isfinite($1.val) && isfinite($3.val))) > > { > > > + $$.val = $1.val / $3.val; > > > + $$.ids = NULL; > > > > hum, I'm confused with this.. compute_ids with finite values? > > why do we erase ids then? also val should be NAN then, no? > > could you please put in some comment with reasoning? > > > > Each expr parsing step needs to create a val and an ids. If we're not > computing ids then we know we don't need ids. If the values are both > constants (aka finite), again we don't need ids as we can just divide. It > is invariant that if you have ids then the value is NAN which isn't finite. > So when computing ids we may want to constant evaluate: > > event1 if 0.5 > 1.0/3.0 else event2 > > which is quite hypothetical but the idea is to have a general approach for > all the operators. The simple lattice is something like: > > Constants: 0.0, 1.0, .... > \. |. / > Bottom: NAN > > Bottom means we really have a set of values and we don't know which it > could be. So: > > 3.0 if event1 > 10.0 else 4.0 > > has possible values of 3.0 or 4.0 which we could represent with the set > {3.0, 4.0}, but because the lattice is simple we just say bottom, meaning > the set of all values - which is conservatively correct as 3.0 and 4.0 are > in the set of all values. It would be incorrect to say the value was 3.0. > Even with a simple lattice we could represent that: > > 3.0 if event1 > 10.0 else 3.0 > > evaluates to 3.0 and so there is no need to measure event1. Note, this > peephole optimization isn't performed here, just the peephole optimization > that if the condition is true or false we can remove events. > > The code in general needs to handle the compute_ids case and the evaluation > case. So what the code is trying to do is propagate constants with sets of > ids in the compute_ids case, or just evaluate in the other case. NAN is > used as a bottom just for simplicity and to avoid inventing a type lattice > abstraction. could you please put it in comment, will be helpful for future ;-) thanks, jirka