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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 11E8EC432C3 for ; Thu, 14 Nov 2019 13:46:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E7A58206F4 for ; Thu, 14 Nov 2019 13:46:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726812AbfKNNq5 (ORCPT ); Thu, 14 Nov 2019 08:46:57 -0500 Received: from mga09.intel.com ([134.134.136.24]:40485 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726254AbfKNNq4 (ORCPT ); Thu, 14 Nov 2019 08:46:56 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Nov 2019 05:46:55 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,304,1569308400"; d="scan'208";a="207792492" Received: from linux.intel.com ([10.54.29.200]) by orsmga003.jf.intel.com with ESMTP; 14 Nov 2019 05:46:55 -0800 Received: from [10.251.18.41] (kliang2-mobl.ccr.corp.intel.com [10.251.18.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by linux.intel.com (Postfix) with ESMTPS id A52175801E3; Thu, 14 Nov 2019 05:46:52 -0800 (PST) Subject: Re: [PATCH v3 10/10] perf/cgroup: Do not switch system-wide events in cgroup switch To: Peter Zijlstra , Ian Rogers Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Andrew Morton , Masahiro Yamada , Kees Cook , Catalin Marinas , Petr Mladek , Mauro Carvalho Chehab , Qian Cai , Joe Lawrence , Tetsuo Handa , Sri Krishna chowdary , "Uladzislau Rezki (Sony)" , Andy Shevchenko , Changbin Du , Ard Biesheuvel , "David S. Miller" , Kent Overstreet , Gary Hook , Arnd Bergmann , linux-kernel@vger.kernel.org, Stephane Eranian , Andi Kleen References: <20191114003042.85252-1-irogers@google.com> <20191114003042.85252-11-irogers@google.com> <20191114104340.GT4131@hirez.programming.kicks-ass.net> From: "Liang, Kan" Message-ID: <710edaf6-2562-0f53-15d6-dc50885b8e08@linux.intel.com> Date: Thu, 14 Nov 2019 08:46:51 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: <20191114104340.GT4131@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/14/2019 5:43 AM, Peter Zijlstra wrote: > On Wed, Nov 13, 2019 at 04:30:42PM -0800, Ian Rogers wrote: >> From: Kan Liang >> >> When counting system-wide events and cgroup events simultaneously, the >> system-wide events are always scheduled out then back in during cgroup >> switches, bringing extra overhead and possibly missing events. Switching >> out system wide flexible events may be necessary if the scheduled in >> task's cgroups have pinned events that need to be scheduled in at a higher >> priority than the system wide flexible events. > > I'm thinking this patch is actively broken. groups->index 'group' wide > and therefore across cpu/cgroup boundaries. > > There is no !cgroup to cgroup hierarchy as this patch seems to assume, > specifically look at how the merge sort in visit_groups_merge() allows > cgroup events to be picked before !cgroup events. No, the patch intends to avoid switch !cgroup during cgroup context switch. In perf_cgroup_switch(), when the cgroup is scheduled out, current implementation schedule out everything including !cgroup. I think it definitely breaks the semantics of !cgroup aka system-wide event. The patch itself doesn't touch the merge sort in visit_groups_merge(). The perf_cgroup_skip_switch() just skips the !cgroup in schedule_in(). Because !cgroup wasn't scheduled out. We don't want to schedule !cgroup in again. The cgroup events must be after !cgroup events, since !cgroup never be switched. Thanks, Kan