linux-kernel - Re: [ltt-dev] Test module : benchmarking read-side locking speed

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Date:	Tue, 26 May 2009 09:33:19 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Steve Langstaff <steve.langstaff@...blebay.com>
Cc:	'David Miller' <davem@...emloft.net>, paulmck@...ux.vnet.ibm.com,
	mingo@...e.hu, jwboyer@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, ltt-dev@...ts.casi.polymtl.ca,
	'Subrata Modak' <tosubrata@...il.com>,
	"'Alan D. Brunelle'" <Alan.Brunelle@...com>,
	'Andika Triwidada' <andika@...rtrek.or.id>
Subject: Re: [ltt-dev] Test module : benchmarking read-side locking speed

* Steve Langstaff (steve.langstaff@...blebay.com) wrote:
> > From: Mathieu Desnoyers [mailto:compudj@...stal.dyndns.org]
> > Sent: 22 May 2009 16:02
> > To: Steve Langstaff
> > Cc: 'David Miller'; paulmck@...ux.vnet.ibm.com; mingo@...e.hu;
> > jwboyer@...ux.vnet.ibm.com; linux-kernel@...r.kernel.org; ltt-
> > dev@...ts.casi.polymtl.ca; 'Subrata Modak'; 'Alan D. Brunelle'; 'Andika
> > Triwidada'
> > Subject: Re: [ltt-dev] Test module : benchmarking read-side locking
> > speed
> > 
> > * Steve Langstaff (steve.langstaff@...blebay.com) wrote:
> > > > From: Mathieu Desnoyers [mailto:compudj@...stal.dyndns.org]
> > > > Sent: 21 May 2009 20:12
> > >
> > >
> > > > I am trying to complete my numbers for performance impact of read-
> > side
> > > > locking primitives (on the fast path) for various architectures.
> > >
> > > > Help with testing on a larger set of architectures would be more
> > than
> > > > welcome. Note that this module requires the kernel to be configured
> > > > with
> > > > CONFIG_PREEMPT=y. Some config option sanity checking is done at
> > > > compile-time. Other requirement : disable invasive lockdep-style
> > > > instrumentation.
> > >
> > > Another requirement is that get_cycles() needs to return something
> > > meaningful :)
> > >
> > 
> > For ARMv7 Omap3, I have the following version (I've been able to get
> > benchmarks with it yesterday). It requires LTTng to be started for the
> > trace clock infrastructure to be in place and running to provide a full
> > 64-bits emulated TSC.
> 
> Using your updated test source, I get slightly different results on my
> PXA255 (total time = 1 rather than 0), but I'm not convinced that the
> measurements are correct...
> 

The LTTng trace clock only uses the cycle counter on ARM OMAP3, AFAIK.
Therefore, the implementation you use is probably using a jiffy-based
method+logical clock (see asm-generic/trace-clock.h). Therefore those
numbers do not represent cycles.

Thanks,

Mathieu

> /lib/modules/2.6.29.2 # insmod ./ltt_test.ko
> [   81.372318] test init
> [   81.374647] Number of active CPUs : 1
> [   81.378806] test results: time for baseline
> [   81.383010] number of loops: 20000
> [   81.386510] total time: 1
> [   81.389147] -> baseline takes 0 cycles
> [   81.392910] test end
> [   81.396017] test results: time for spinlock
> [   81.400292] number of loops: 20000
> [   81.403711] total time: 1
> [   81.406417] -> spinlock takes 0 cycles
> [   81.410184] test end
> [   81.413293] test results: time for read rwlock
> [   81.417825] number of loops: 20000
> [   81.421248] total time: 1
> [   81.423887] -> read rwlock takes 0 cycles
> [   81.427990] test end
> [   81.430844] test results: time for seqlock
> [   81.434962] number of loops: 20000
> [   81.438439] total time: 1
> [   81.441075] -> seqlock takes 0 cycles
> [   81.444751] test end
> [   81.447871] test results: time for preempt disable/enable pairs
> [   81.453818] number of loops: 20000
> [   81.457300] total time: 1
> [   81.459940] -> preempt disable/enable pair takes 0 cycles
> [   81.465359] test end
> insmod: cannot insert './ltt_test.ko': Resource temporarily unavailable
> (-1): Resource temporarily unavailable
> 
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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