linux-kernel - Re: [PATCH] slub: reduce overhead of slub

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Date:	Thu, 07 Jul 2011 13:55:59 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, rientjes@...gle.com,
	linux-mm@...ck.org
Subject: Re: [PATCH] slub: reduce overhead of slub_debug

On Thu, 2011-07-07 at 21:52 +0300, Pekka Enberg wrote:
> On Thu, 7 Jul 2011, Pekka Enberg wrote:
> > > Looks good to me. Christoph, David, ?
> 
> On Thu, 2011-07-07 at 13:17 -0500, Christoph Lameter wrote:
> > The reason debug code is there is because it is useless overhead typically
> > not needed. There is no point in optimizing the code that is not run in
> > production environments unless there are gross performance issues that
> > make debugging difficult. A performance patch for debugging would have to
> > cause significant performance improvements. This patch does not do that
> > nor was there such an issue to be addressed in the first place.
> 
> Is there something technically wrong with the patch? Quoting the patch
> email:
> 
>   (Compiling some project with different options)
>                                  make -j12    make clean
>   slub_debug disabled:             1m 27s       1.2 s
>   slub_debug enabled:              1m 46s       7.6 s
>   slub_debug enabled + this patch: 1m 33s       3.2 s
> 
>   check_bytes still shows up high, but not always at the top.
> 
> That's significant enough speedup for me!

We're not going to make any progress on this; Christoph conveniently
forgets the counterarguments from week to week.

-- 
Mathematics is the supreme nostalgia of our time.


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