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,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 2B0F5C433B4 for ; Fri, 16 Apr 2021 10:29:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0E2661002 for ; Fri, 16 Apr 2021 10:29:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235101AbhDPK3A (ORCPT ); Fri, 16 Apr 2021 06:29:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46092 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229719AbhDPK26 (ORCPT ); Fri, 16 Apr 2021 06:28:58 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63F27C061574 for ; Fri, 16 Apr 2021 03:28:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=CWrS5XSLYo4ciqDUEjhD1jnthccxk9YJcxF+IcCqVhY=; b=ADPdO0BxVbJOyovTHpfTPOoKum gDDMTFcJNFsxXDMtyOJAmVgqMEGklqUx97H8S4cC071lxCG66pLtoWaEitLNB6SrAmdckWFLrSCHA kSkWP5ztBXQS+YVREZ3kPWqCxmY9jFUUEtABuSGUNyIOQ79NTeYlVVJA5kq7MS6YFVUh9c2gIxfWL eGIalbTXqZTUlbHSGFGuBz1xnT0rPe5hBNZPcUWnqn50zPyf9NppjoEBXNZKTMguqswD+NjhpVXQL cqnALhnG+ZsKt1Laxzz0wojtxtvASN44/j4+pmWlvVoPmTYgknNMLsIJnDq8UROox0XnQytdQ/vAu K9eqFn+g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lXLhd-009omq-H4; Fri, 16 Apr 2021 10:28:00 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 3B426300212; Fri, 16 Apr 2021 12:27:56 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 043DD200C8D28; Fri, 16 Apr 2021 12:27:55 +0200 (CEST) Date: Fri, 16 Apr 2021 12:27:55 +0200 From: Peter Zijlstra To: Namhyung Kim Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Jiri Olsa , Mark Rutland , Alexander Shishkin , LKML , Stephane Eranian , Andi Kleen , Ian Rogers , Song Liu , Tejun Heo , kernel test robot , Thomas Gleixner Subject: Re: [PATCH v3 1/2] perf/core: Share an event with multiple cgroups Message-ID: References: <20210413155337.644993-1-namhyung@kernel.org> <20210413155337.644993-2-namhyung@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 16, 2021 at 11:29:30AM +0200, Peter Zijlstra wrote: > > So I think we've had proposals for being able to close fds in the past; > > while preserving groups etc. We've always pushed back on that because of > > the resource limit issue. By having each counter be a filedesc we get a > > natural limit on the amount of resources you can consume. And in that > > respect, having to use 400k fds is things working as designed. > > > > Anyway, there might be a way around this.. So how about we flip the whole thing sideways, instead of doing one event for multiple cgroups, do an event for multiple-cpus. Basically, allow: perf_event_open(.pid=fd, cpu=-1, .flag=PID_CGROUP); Which would have the kernel create nr_cpus events [the corrolary is that we'd probably also allow: (.pid=-1, cpu=-1) ]. Output could be done by adding FORMAT_PERCPU, which takes the current read() format and writes a copy for each CPU event. (p)read(v)() could be used to explode or partial read that. This gets rid of the nasty variadic nature of the 'get-me-these-n-cgroups'. While still getting rid of the n*m fd issue you're facing.