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=-6.0 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 C232AC433E0 for ; Wed, 17 Mar 2021 09:20:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8C7EB64EF2 for ; Wed, 17 Mar 2021 09:20:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229808AbhCQJTu (ORCPT ); Wed, 17 Mar 2021 05:19:50 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34206 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229796AbhCQJTi (ORCPT ); Wed, 17 Mar 2021 05:19:38 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615972778; 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=wDtR7tgXN0GWY9XTaXa4dXAdEOCAehc3gkBXn58TQJU=; b=L5jmj0L9bQL0WVo6FCNzkZkCjWgQ+gS7jEmP0ygb9/SAIhWOYmVZo4z94Cns4xE5SHDtnj Ja8Fzu+4n2Db5lRzKFv6dtm4dycIXxh1Ade6nxQIIyJmYjYG6igKyXa72oZWZsDZwkLIbs A0SlbUIeHw3X/h6QC3qzTpViKlJ3y58= 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-283-GAaik-TOMr6ZaUl5Ha7XGw-1; Wed, 17 Mar 2021 05:19:34 -0400 X-MC-Unique: GAaik-TOMr6ZaUl5Ha7XGw-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 B3F2E81746B; Wed, 17 Mar 2021 09:19:32 +0000 (UTC) Received: from krava (unknown [10.40.194.149]) by smtp.corp.redhat.com (Postfix) with SMTP id E88CA5C23E; Wed, 17 Mar 2021 09:19:30 +0000 (UTC) Date: Wed, 17 Mar 2021 10:19:29 +0100 From: Jiri Olsa To: Namhyung Kim Cc: Song Liu , linux-kernel , Kernel Team , Arnaldo Carvalho de Melo , Arnaldo Carvalho de Melo , Jiri Olsa Subject: Re: [PATCH v2 0/3] perf-stat: share hardware PMCs with BPF Message-ID: References: <20210316211837.910506-1-songliubraving@fb.com> 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 Wed, Mar 17, 2021 at 02:29:28PM +0900, Namhyung Kim wrote: > Hi Song, > > On Wed, Mar 17, 2021 at 6:18 AM Song Liu wrote: > > > > perf uses performance monitoring counters (PMCs) to monitor system > > performance. The PMCs are limited hardware resources. For example, > > Intel CPUs have 3x fixed PMCs and 4x programmable PMCs per cpu. > > > > Modern data center systems use these PMCs in many different ways: > > system level monitoring, (maybe nested) container level monitoring, per > > process monitoring, profiling (in sample mode), etc. In some cases, > > there are more active perf_events than available hardware PMCs. To allow > > all perf_events to have a chance to run, it is necessary to do expensive > > time multiplexing of events. > > > > On the other hand, many monitoring tools count the common metrics (cycles, > > instructions). It is a waste to have multiple tools create multiple > > perf_events of "cycles" and occupy multiple PMCs. > > Right, it'd be really helpful when the PMCs are frequently or mostly shared. > But it'd also increase the overhead for uncontended cases as BPF programs > need to run on every context switch. Depending on the workload, it may > cause a non-negligible performance impact. So users should be aware of it. right, let's get get some idea of how bad that actualy is Song, could you please get some numbers from runnning for example 'perf bench sched messaging ...' with both normal and bpf mode perf stat? for all supported target options thanks, jirka