From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754069AbaIHOFi (ORCPT ); Mon, 8 Sep 2014 10:05:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34192 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753327AbaIHOFg (ORCPT ); Mon, 8 Sep 2014 10:05:36 -0400 Date: Mon, 8 Sep 2014 16:04:54 +0200 From: Jiri Olsa To: Arnaldo Carvalho de Melo Cc: Adrian Hunter , linux-kernel@vger.kernel.org, David Ahern , Don Zickus , Frederic Weisbecker , Mike Galbraith , Namhyung Kim , Paul Mackerras , Peter Zijlstra , Stephane Eranian Subject: Re: [PATCH 04/10] perf record: Filter out POLLHUP'ed file descriptors Message-ID: <20140908140454.GF17728@krava.brq.redhat.com> References: <1409781604-16778-1-git-send-email-acme@kernel.org> <1409781604-16778-5-git-send-email-acme@kernel.org> <54085BC8.40403@intel.com> <20140904151902.GE2997@kernel.org> <54097793.4050201@intel.com> <20140905140756.GD30520@kernel.org> <20140906203915.GA9843@krava.brq.redhat.com> <20140908134615.GD2773@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140908134615.GD2773@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 08, 2014 at 10:46:16AM -0300, Arnaldo Carvalho de Melo wrote: > Em Sat, Sep 06, 2014 at 10:39:15PM +0200, Jiri Olsa escreveu: > > On Fri, Sep 05, 2014 at 11:07:56AM -0300, Arnaldo Carvalho de Melo wrote: > > > Em Fri, Sep 05, 2014 at 11:42:59AM +0300, Adrian Hunter escreveu: > > > > On 09/04/2014 06:19 PM, Arnaldo Carvalho de Melo wrote: > > > > > Em Thu, Sep 04, 2014 at 03:32:08PM +0300, Adrian Hunter escreveu: > > > > No I was meaning something different. For example, 'perf record' opens an > > > > event for 2 processes per-cpu and gets 4 file descriptors: > > > > > task1 task2 > > > > cpu0 fd0 fd1 > > > > cpu1 fd2 fd3 > > > > > Now, perf record will mmap fd0 and fd2 and set-output fd1->fd0 > > > > and fd3->fd2. > > > > > pollfds includes only fd0 and fd2. > > > > > But if task2 exits, the POLLHUP will appear on fd1 and fd3. > > > > So? We are not interested in fd1 and fd3, since all our reading is done > > > on fd0 and fd2 mmaps, no? > > > hm, what if task1 (fd0, fd2) exits first.. perf record will exit, > > but it still has to read task2..? > > Ok, what happens in that case, i.e. when the fds that were set to be the > ones to be polled, gets nuked, does the set-output command gets just > undone? Or does the mmap stands, receiving the events from the remaining > fds and the polling notifications get sent to, in this case, fd3 and > fd1? mmaps stays for fd1 and fd3.. and they get poll notifications as well, we just do not check/poll them now > > I'll look at the kernel code for that... > > > > I.e. when we ask the kernel to point fd B to fd A's mmap (what you > > > called set-output) and fd B inserts an event into fd A's mmap ring > > > buffer, we get fd A poll return as POLLRD, no? > > > > Have to check... Otherwise we would have to poll all fds all the time, > > > not just the ones mmaping, right? > > > > > I think Jiri's patchset changed pollfds to include all fds for that reason. > > > hm, I did not think of that.. ;-) I needed more grained feedback > > for future features like cpu hotplug > > So this is good for something you didn't tried to fix (and document) but > good for something that may be nice in the future? Grumpf, we have > already way too much stuff that will be eventually used but is not used > right now :-\ > IMO it's more clear to poll pm all event FDs.. and now with the case Adrian described it seems necessary anyway jirka