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=-3.9 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 D63A1C433E7 for ; Mon, 19 Oct 2020 20:15:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5FF6F223FB for ; Mon, 19 Oct 2020 20:15:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ZKQIo0EN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730674AbgJSUPy (ORCPT ); Mon, 19 Oct 2020 16:15:54 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55106 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726118AbgJSUPx (ORCPT ); Mon, 19 Oct 2020 16:15:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603138552; 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=N82ij3z3wbxQGuGAW3gzlLhzS6s/KSiyU/Pt8sLH0lA=; b=ZKQIo0ENw/IZ1i9w/Kdw9OXR8jwg+iKaDRkkeO17aUeL2Xq6D0KiHpy8aJeN2KkYmIlCRW xY4Y6BfUB69ViZ6YrJjY+U2f9+tqPLZ5Fsa0HYwOEmeJrzUQSd49K8YgqmZ01TVWgCUCvd 1JpaTaf9my5lWyR1AP47Ym+R7L4o/9o= 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-511-IN3r4lUjPx2zCiAQe25bGg-1; Mon, 19 Oct 2020 16:15:48 -0400 X-MC-Unique: IN3r4lUjPx2zCiAQe25bGg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6280E1006C83; Mon, 19 Oct 2020 20:15:45 +0000 (UTC) Received: from krava (unknown [10.40.194.190]) by smtp.corp.redhat.com (Postfix) with SMTP id 3906950B44; Mon, 19 Oct 2020 20:15:42 +0000 (UTC) Date: Mon, 19 Oct 2020 22:15:41 +0200 From: Jiri Olsa To: Rob Herring Cc: Will Deacon , Catalin Marinas , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , linux-arm-kernel , "linux-kernel@vger.kernel.org" , Alexander Shishkin , Namhyung Kim , Raphael Gault , Mark Rutland , Jonathan Cameron , Ian Rogers , Honnappa Nagarahalli , Itaru Kitayama Subject: Re: [PATCH v4 4/9] libperf: Add libperf_evsel__mmap() Message-ID: <20201019201541.GN1461394@krava> References: <20201001140116.651970-1-robh@kernel.org> <20201001140116.651970-5-robh@kernel.org> <20201014110527.GA1349644@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 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 16, 2020 at 04:39:15PM -0500, Rob Herring wrote: > On Wed, Oct 14, 2020 at 6:05 AM Jiri Olsa wrote: > > > > On Thu, Oct 01, 2020 at 09:01:11AM -0500, Rob Herring wrote: > > > > SNIP > > > > > > > > +void *perf_evsel__mmap(struct perf_evsel *evsel, int pages) > > > +{ > > > + int ret; > > > + struct perf_mmap *map; > > > + struct perf_mmap_param mp = { > > > + .prot = PROT_READ | PROT_WRITE, > > > + }; > > > + > > > + if (FD(evsel, 0, 0) < 0) > > > + return NULL; > > > + > > > + mp.mask = (pages * page_size) - 1; > > > + > > > + map = zalloc(sizeof(*map)); > > > + if (!map) > > > + return NULL; > > > + > > > + perf_mmap__init(map, NULL, false, NULL); > > > + > > > + ret = perf_mmap__mmap(map, &mp, FD(evsel, 0, 0), 0); > > > > hum, so you map event for FD(0,0) but later in perf_evsel__read > > you allow to read any cpu/thread combination ending up reading > > data from FD(0,0) map: > > > > int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread, > > struct perf_counts_values *count) > > { > > size_t size = perf_evsel__read_size(evsel); > > > > memset(count, 0, sizeof(*count)); > > > > if (FD(evsel, cpu, thread) < 0) > > return -EINVAL; > > > > if (evsel->mmap && !perf_mmap__read_self(evsel->mmap, count)) > > return 0; > > > > > > I think we should either check cpu == 0, thread == 0, or make it > > general and store perf_evsel::mmap in xyarray as we do for fds > > The mmapped read will actually fail and then we fallback here. My main > concern though is adding more overhead on a feature that's meant to be > low overhead (granted, it's not much). Maybe we could add checks on > the mmap that we've opened the event with pid == 0 and cpu == -1 (so > only 1 FD)? but then you limit this just for single fd.. having mmap as xyarray would not be that bad and perf_evsel__mmap will call perf_mmap__mmap for each defined cpu/thread .. so it depends on user how fast this will be - how many maps needs to be created/mmaped jirka