Subject: Re: [Bugme-new] [Bug 12562] New: High overhead while switching or
 synchronizing threads on different cores
From: Thomas Pilarski <thomas.pi@arcor.de>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>, Mike Galbraith <efault@gmx.de>,
       Gregory Haskins <ghaskins@novell.com>, bugme-daemon@bugzilla.kernel.org,
       linux-kernel@vger.kernel.org
In-Reply-To: <1233229028.4495.34.camel@laptop>
References: <bug-12562-10286@http.bugzilla.kernel.org/>
	 <20090128125604.94ed3fe0.akpm@linux-foundation.org>
	 <1233181507.6988.14.camel@bugs-laptop>  <1233220048.7835.19.camel@twins>
	 <1233223979.5294.41.camel@bugs-laptop>
	 <1233224644.5294.52.camel@bugs-laptop>  <1233229028.4495.34.camel@laptop>
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Date: Thu, 29 Jan 2009 15:05:34 +0100
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> In short this program is carefully crafted to defeat all our affinity
> tests - and I'm not sure what to do.

I am sorry, although it is not carefully crafted. The function random()
is causing my problem. I currently have no real data, so I tried to make
some random utilization and data.

Without the random() function it works even with 80MB of data and I get
great results.

./ThreadSchedulingIssue 1 10485760 8 312
All threads finished: 309 messages in 29.369 seconds / 10.521 msg/s

schedtool -a 1 -e ./ThreadSchedulingIssue 1 10485760 8 312
All threads finished: 312 messages in 44.284 seconds / 7.045 msg/s

It does not even regress with more then two threads. 

./ThreadSchedulingIssue 2 10485760 8 312
All threads finished: 311 messages in 28.040 seconds / 11.091 msg/s

./ThreadSchedulingIssue 4 10485760 8 312
All threads finished: 309 messages in 28.021 seconds / 11.027 msg/s

With small amounts of data the speed on two core is even doubled. 

schedtool -a 1 -e ./ThreadSchedulingIssue 1 1048 8 312000
All threads finished: 311992 messages in 19.437 seconds / 16051.247
msg/s

./ThreadSchedulingIssue 3 1048 8 312000
All threads finished: 311998 messages in 9.652 seconds / 32324.411 msg/s

./ThreadSchedulingIssue 8 1048 8 312000
All threads finished: 311997 messages in 9.339 seconds / 33406.370 msg/s

--------------
Perhaps it is as it should be, but when I run the test (without
random()) with 2*8 threads, it uses ~186 of the cpu, while an instance
of "bzip2 -9 -c /dev/urandom >/dev/null" gets only 12%.

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