linux-kernel - Re: [PATCH] radeon: preallocate memory for command stream parsing

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Date:	Wed, 24 Jun 2009 10:29:01 +0200
From:	Jerome Glisse <glisse@...edesktop.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Jerome Glisse <jglisse@...hat.com>, Nick Piggin <npiggin@...e.de>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.sf.net
Subject: Re: [PATCH] radeon: preallocate memory for command stream parsing

On Tue, 2009-06-23 at 22:52 +0300, Pekka Enberg wrote:
> Hi Jerome,
> 
> On Tue, Jun 23, 2009 at 10:46 PM, Jerome Glisse<jglisse@...hat.com> wrote:
> > Command stream parsing is the most common operation and can
> > happen hundred of times per second, we don't want to allocate/free
> > memory each time this ioctl is call. This rework the ioctl
> > to avoid doing so by allocating temporary memory along the
> > ib pool.
> >
> > Signed-off-by: Jerome Glisse <jglisse@...hat.com>
> 
> So how much does this help (i.e. where are the numbers)? I am bit
> surprised "hundred of times per second" is an issue for our slab
> allocators. Hmm?
> 

I didn't have real number but the vmap path was really slower,
quake3 fps goes from ~20 to ~40 on average when going from vmap
to preallocated. When using kmalloc i don't thing there was so
much performance hit. But i think the biggest hit was that in
previous code i asked for zeroed memory so i am pretty sure kernel
spend a bit of time clearing page. I reworked the code to avoid
needing cleared memory and so avoid memset, this is likely why
we get a performance boost.

Cheers,
Jerome

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