agp/intel: Fix the pre-9xx chipset flush.

Commit Message

Brice Goglin Sept. 11, 2009, 6:34 a.m. UTC

Eric Anholt wrote:
> The chipset flush was on the right track -- hitting the right amount of
> memory, and it appears to be the only way to flush on these chipsets, but the
> flush page was mapped uncached.  As a result, the writes trying to clear the
> writeback cache ended up bypassing the cache, and not flushing anything!  The
> wbinvd would flush out other writeback data and often cause the data we wanted
> to get flushed, but not always.  By removing the setting of the page to UC
> and instead just clflushing the data we write to try to flush it, we get the
> desired behavior with no wbinvd. 
>   

This helps a lot, thanks Eric. I've been running various things under
metacity and compiz during the last 10mn without problems while X would
usually hang after 10s. But I needed the below patch to build the
intel-agp driver as a module.

Signed-off-by: Brice Goglin <[e-mail]>

Comments

Eric Anholt Sept. 11, 2009, 6:37 p.m. UTC | #1

On Fri, 2009-09-11 at 08:34 +0200, Brice Goglin wrote:
> Eric Anholt wrote:
> > The chipset flush was on the right track -- hitting the right amount of
> > memory, and it appears to be the only way to flush on these chipsets, but the
> > flush page was mapped uncached.  As a result, the writes trying to clear the
> > writeback cache ended up bypassing the cache, and not flushing anything!  The
> > wbinvd would flush out other writeback data and often cause the data we wanted
> > to get flushed, but not always.  By removing the setting of the page to UC
> > and instead just clflushing the data we write to try to flush it, we get the
> > desired behavior with no wbinvd. 
> >   
> 
> This helps a lot, thanks Eric. I've been running various things under
> metacity and compiz during the last 10mn without problems while X would
> usually hang after 10s. But I needed the below patch to build the
> intel-agp driver as a module.

Thanks!

Patch

Index: linux-2.6.31/arch/x86/mm/pageattr.c
===================================================================
--- linux-2.6.31.orig/arch/x86/mm/pageattr.c	2009-09-11 08:02:14.000000000 +0200
+++ linux-2.6.31/arch/x86/mm/pageattr.c	2009-09-11 08:02:48.000000000 +0200
@@ -143,6 +143,7 @@ 
 
 	mb();
 }
+EXPORT_SYMBOL_GPL(clflush_cache_range);
 
 static void __cpa_flush_all(void *arg)
 {