linux-kernel - Re: [PATCH] SLUB use cmpxchg

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Message-ID: <20070822002616.GA1400@Krystal>
Date:	Tue, 21 Aug 2007 20:26:16 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Christoph Lameter <clameter@....com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com
Subject: Re: [PATCH] SLUB use cmpxchg_local

* Christoph Lameter (clameter@....com) wrote:
> On Tue, 21 Aug 2007, Mathieu Desnoyers wrote:
> 
> > - Rounding error.. you seem to round at 0.1ms, but I keep the values in
> >   cycles. The times that you get (1.1ms) seems strangely higher than
> >   mine, which are under 1000 cycles on a 3GHz system (less than 333ns).
> >   I guess there is both a ms - ns error there and/or not enough
> >   precision in your numbers.
> 
> Nope the rounding for output is depending on the amount. Rounds to one 
> digit after whatever unit we figured out is best to display.
> 
> And multiplications (cyc2ns) do not result in rounding errors.
> 

Ok, I see now that the 1.1ms was for the 10000 iterations, which makes
it about 230 ns/iteration for the 10000 times kmalloc(8) = 2.3ms test.

As I am going back through the initial cmpxchg_local implementation, it
seems like it was executing __slab_alloc() with preemption disabled,
which is wrong. new_slab() is not designed for that.

I'll try to run my tests on AMD64.

Mathieu

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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