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Date: Wed, 8 Mar 2017 17:48:53 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: pthread_create() slowdown with concurrent sched_yield()
Message-ID: <20170308164853.GA1559@calimero.vinschen.de>
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On Mar  7 16:19, Dan Bonachea wrote:
> I suspect I may have discovered a corner-case performance bug in
> Cygwin's pthread_create() implementation. The problem arises when a
> call to pthread_create() is made concurrently with multiple pthreads
> in the same process spinning on calls to sched_yield(). I've searched
> the Cygwin mailing list archives, user guide, FAQ, and Google and not
> found any mention of this particular misbehavior.
>=20
> A minimal demo program is copied below and also available here:
>    https://upc-bugs.lbl.gov/bugzilla/attachment.cgi?id=3D549
> The demo program is a narrowed-down version of test code used in the
> GASNet communication system (http://gasnet.lbl.gov).
>=20
> The test code calls pthread_create to spawn a user-controlled number
> of threads, which then execute 1000 "spin barriers" - implemented by
> spinning on in-memory flags and stalling with sched_yield(). The test
> can also optionally insert a pthread_barrier_wait() across all threads
> before the first spin barrier.

Thanks for the thorough analysis and especially the testcase!

I applied a fix for this problem and uploaded new developer snapshots
to https://cygwin.com/snapshots/

Please give them a try.


Thanks,
Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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