X-Recipient: archive-cygwin AT delorie DOT com
X-SWARE-Spam-Status: No, hits=-1.6 required=5.0	tests=AWL,BAYES_00,KHOP_RCVD_UNTRUST,KHOP_THREADED,RCVD_IN_DNSWL_LOW,SPF_NEUTRAL,T_RP_MATCHES_RCVD
X-Spam-Check-By: sourceware.org
Message-ID: <4FDA3917.20309@cs.utoronto.ca>
Date: Thu, 14 Jun 2012 15:18:47 -0400
From: Ryan Johnson <ryan DOT johnson AT cs DOT utoronto DOT ca>
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20120428 Thunderbird/12.0.1
MIME-Version: 1.0
To: cygwin AT cygwin DOT com
Subject: Re: Performance problems with emacs-X11 in current cygwin
References: <4FCB2991 DOT 3010701 AT users DOT sourceforge DOT net> <4FCB5438 DOT 7080903 AT cornell DOT edu> <4FCB9872 DOT 5010506 AT cornell DOT edu> <loom DOT 20120606T123651-460 AT post DOT gmane DOT org> <4FD1F709 DOT 4050107 AT cornell DOT edu> <87k3zhbyyk DOT fsf AT Rainer DOT invalid> <4FD22C39 DOT 6070107 AT cornell DOT edu> <4FD53FA9 DOT 2040105 AT cornell DOT edu> <4FD8DE9C DOT 1090900 AT cornell DOT edu> <4FD90105 DOT 7050701 AT cornell DOT edu> <20120613214043 DOT GA3554 AT ednor DOT casa DOT cgf DOT cx>
In-Reply-To: <20120613214043.GA3554@ednor.casa.cgf.cx>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-IsSubscribed: yes
Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id: <cygwin.cygwin.com>
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com

On 13/06/2012 5:40 PM, Christopher Faylor wrote:
> On Wed, Jun 13, 2012 at 05:07:17PM -0400, Ken Brown wrote:
>> On 6/13/2012 2:40 PM, Ken Brown wrote:
>>> On 6/10/2012 8:45 PM, Ken Brown wrote:
>>>> The bisection shows that the first problematic commit is this one:
>>>>
>>>> http://git.gnome.org/browse/glib/commit/?h=glib-2-32&id=7eae486179e2799c369ed9ffcea663bf9161ce79
>>>>
>>>>
>>>>
>>>> Author: Ryan Lortie<desrt AT desrt DOT ca>
>>>> Date: Wed Aug 31 22:07:02 2011 -0400
>>>>
>>>> GMain: simplify logic for g_wakeup_acknowledge()
>>>>
>>>> Instead of messing around with context->poll_waiting, just look at the
>>>> GPollFD to see if the GWakeup needs to be acknowledged.
>>> I think this commit contains a typo: "events" should be "revents".
>>> (context->wake_up_rec.events is always nonzero at this point in the
>>> code, so it makes no sense to test that.) As a result,
>>> g_wakeup_acknowledge() is being called much more often than necessary. I
>>> think this could easily explain the performance problems that have been
>>> reported, but I won't have a chance to test this on my (slow) XP system
>>> for a while, and possibly not until tomorrow.
>> I've confirmed that fixing the typo solves the problem on my XP system.
>>   I suspect that this issue is not specific to XP after all and has more
>> to do with the slowness of the machine, so that the performance problem
>> is more noticeable.  In any case, it's clearly a glib bug.
>>
>> I've filed a bug report upstream:
>>
>>    https://bugzilla.gnome.org/show_bug.cgi?id=678052
> What incredible perseverence you've shown in tracking this down.  Bravo!
++

Amazing. This is one of the nastier kinds of bugs I've seen anybody 
track down... bug not where anybody thinks it is, and in library code 
generally assumed to be robust, bisecting the monster that is glibc, bug 
hunter knows (or willing to learn) glibc well enough to tell what 
revents and events do (and that revents even exists!), but not so well 
that the eyes glossed over the typo.

Ironically, the 'r' key on my laptop has been acting up lately, so I can 
totally relate to the poor fellow who tried to type 'revents' and didn't 
notice when 'events' compiled and checked in instead...

Ryan


--
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