linux-kernel - Re: AGP and PAT (induced?) problem (on AMD family 6)

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Message-ID: <20080819190757.GA17470@linux-os.sc.intel.com>
Date:	Tue, 19 Aug 2008 12:07:57 -0700
From:	Venki Pallipadi <venkatesh.pallipadi@...el.com>
To:	Rene Herman <rene.herman@...access.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Dave Airlie <airlied@...il.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Arjan van de Ven <arjan@...radead.org>,
	"dri-users@...ts.sourceforge.net" <dri-users@...ts.sourceforge.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: AGP and PAT (induced?) problem (on AMD family 6)

On Tue, Aug 19, 2008 at 07:19:44AM -0700, Rene Herman wrote:
> On 19-08-08 12:26, Ingo Molnar wrote:
> 
> > * Rene Herman <rene.herman@...access.nl> wrote:
> >
> >> On 15-08-08 17:24, Rene Herman wrote:
> >>
> >>> On 15-08-08 16:22, Ingo Molnar wrote:
> >>>
> >>>> (more people Cc:-ed)
> >>> Thank you. Additional information at http://lkml.org/lkml/2008/8/6/449
> >>>
> >>>> agreed - +12 seconds wait suggest some rather fundamental breakage.
> >>>> Did we go back to uncached for some critical display area that makes
> >>>> X start up (shut down) that slowly? Did we mark the BIOS uncacheable
> >>>> perhaps, causing X to execute BIOS code very slowly?
> >>> Quite a lot "uncached-minus" in those lists. I am desperately trying to
> >>> avoid a clue about mostly anything graphics related so, "I dunno".
> >>>
> >>> I haven't just disabled PAT yet (although I was about to just do so)
> >>> and am available for testing.
> >> <waiting with bated breath>
> >>
> >> Additional observation with respect to first,next shutdown:
> >>
> >> With Option "AGPSize" "64", and booted with "nopat", X startup (from
> >> startx<enter> to functional desktop) is approximately 5 seconds,
> >> shutdown is 1 second as calibration times.
> >>
> >> Booted without "nopat", X startup seems to alternate between 10+ and
> >> 16+ seconds and for shutdown -- the first shutdown after boot takes
> >> some 14 seconds total, subsequent shutdowns settle at around 5
> >> seconds.
> >
> > would it be possible to start up and shut down X in the slow case via
> > strace, by doing something like this:
> >
> >   strace -f -ttt -TTT -o trace.log startx
> >
> > and see which system calls (or other activities) took suspiciously long?
> 
> It wouldn't it seems. Root X (needed for the strace) works fine but
> started this way hangs indefinitely.
> 
> I believe the 14 seconds for first shutdown to 5 later might be telling.
> Sounds like something might have fixed up uncached entries.
> 
> I'd really like a reply from the AGP or PAT side right about now.
> 

Hmm. Looks like there are more than 16000 entries in the PAT list!

This delay may be due to the overhead of parsing this linked list everytime
for a new entry, rather than any problem with cache setting itself.

I am working on a patch to optimize this pat list parsing for the simple case.
Should be able to send it out later today, for testing.

Thanks,
Venki

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