linux-kernel - Re: io resources and cached mappings (was: [git pull] drm patches for 2.6.27-rc1)

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Message-ID: <20081022093615.GF12453@elte.hu>
Date:	Wed, 22 Oct 2008 11:36:15 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Keith Packard <keithp@...thp.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Dave Airlie <airlied@...ux.ie>,
	Yinghai Lu <yinghai@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.sf.net, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: io resources and cached mappings (was: [git pull] drm patches
	for 2.6.27-rc1)


* Keith Packard <keithp@...thp.com> wrote:

> On Mon, 2008-10-20 at 13:58 +0200, Ingo Molnar wrote:
> 
> > yes but note that by caching the whole mapping on 64-bit we get 
> > everything we want: trivially lockless, works from any CPU, can be 
> > preempted at will, and there are no ugly INVLPG flushes anywhere.
> 
> I was assuming that on 64-bit, the map would be created at driver init 
> time and be left in place until the driver closed; if that's what you 
> mean by 'caching', then yes, we should cache the map.

correct.

> > 32-bit we should handle as well but not design for it.
> 
> As long as we get kmap_atomic-like performance, and we get to simplify 
> our code, I'm up for it.

okay. So ... mind sending your io_mapping patch as a generic facility? 
It looks all good to me in its present form, except that it should live 
in include/linux/io.h, not in the drivers/gpu/drm/i915/io_reserve.h file
:-)

also, please send at least two patches, so that we can look at (and 
possibly merge) the generic facility in isolation.

	Ingo
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