From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 28241 invoked by alias); 21 Apr 2017 12:08:40 -0000 Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Received: (qmail 28219 invoked by uid 89); 21 Apr 2017 12:08:39 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-0.3 required=5.0 tests=AWL,BAYES_50,RCVD_IN_DNSWL_LOW,RP_MATCHES_RCVD,SPF_PASS autolearn=ham version=3.3.2 spammy=humble, ended, Geisert, geisert X-HELO: sasl.smtp.pobox.com Received: from pb-smtp2.pobox.com (HELO sasl.smtp.pobox.com) (64.147.108.71) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Fri, 21 Apr 2017 12:08:37 +0000 Received: from sasl.smtp.pobox.com (unknown [127.0.0.1]) by pb-smtp2.pobox.com (Postfix) with ESMTP id D30438472B for ; Fri, 21 Apr 2017 08:08:37 -0400 (EDT) Received: from pb-smtp2.nyi.icgroup.com (unknown [127.0.0.1]) by pb-smtp2.pobox.com (Postfix) with ESMTP id C9A4584729 for ; Fri, 21 Apr 2017 08:08:37 -0400 (EDT) Received: from [192.168.1.4] (unknown [76.215.41.237]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by pb-smtp2.pobox.com (Postfix) with ESMTPSA id 3A8EC84728 for ; Fri, 21 Apr 2017 08:08:37 -0400 (EDT) Subject: Re: long I/O delays when strace is running To: cygwin@cygwin.com References: <91DCAC3CB99C724EB365BB64677FBE7B16EBBD@MX204CL04.corp.emc.com> <46e39bce-9782-5c74-c196-35ee97ebbc64@pobox.com> <58F9D314.2000100@maxrnd.com> From: Daniel Santos Message-ID: <7d56e728-32a3-9179-b002-e83880e297d0@pobox.com> Date: Fri, 21 Apr 2017 18:23:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <58F9D314.2000100@maxrnd.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Pobox-Relay-ID: 3FF18C5C-268B-11E7-9891-C260AE2156B6-06139138!pb-smtp2.pobox.com X-IsSubscribed: yes X-SW-Source: 2017-04/txt/msg00266.txt.bz2 On 04/21/2017 04:38 AM, Mark Geisert wrote: > > I can reproduce your issue on a real Win7.64 machine so that removes > any possible virtual machine root cause. I was running 'top -s1' in > one window while running your testcase in another window. Yes, top > froze for many seconds at a time, then caught its display up, only to > freeze again repeatedly. It was still frozen for a while after your > testcase had ended (!), then caught up. Your mention of pinfo::init > and 'ps' along with my usage of 'top' leads me to think this may be > somehow related to the /proc filesystem. > > Here's my humble contribution to the discussion: > > ~ time w > 02:15:52 up 3 days, 20:34, 0 users, load average: 0.99, 0.62, 0.31 > USER TTY LOGIN@ IDLE JCPU PCPU WHAT > > real 0m0.203s <-- OK, nice and fast > user 0m0.077s > sys 0m0.139s > > ~ time strace -o w.out w > 02:16:23 up 3 days, 20:34, 0 users, load average: 0.54, 0.55, 0.29 > USER TTY LOGIN@ IDLE JCPU PCPU WHAT > > real 0m28.487s <-- but stracing it is much, much slower > user 0m0.015s > sys 0m0.000s > > The 'w' command is normally pretty fast. Running it under strace > makes it take an unreasonably long time. Something seems busted > somewhere. The strace output for this example has many occurrences of > ~3.1-second delays that seem to occur as w is accumulating process > time information for all processes. > > ..mark Thanks for the help Mark. My current suspicion is that the _pinfo isn't getting initialized when the process is exec-ed by strace, but I haven't proved that. I added a dump() member function to _pinfo, but it crashes and I can't seem to debug that in gdb (it makes a stacktrace file instead of letting me debug). So the cygpid. shared object is there, but I'm suspecting that it's either all zeros or just not fully initialized -- and this is for the pid of the strace process. So for each strace process, there's a 2-3 second delay when trying to read the process list. Daniel -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple