Re: [Bug 10328] New: [regression] performance drop for glx

[Arjan van de Ven]

Suresh Siddha wrote:
> On Tue, Mar 25, 2008 at 03:28:09PM -0700, Andrew Morton wrote:
> > (switched to email.  Please respond via emailed reply-to-all, not via the
> > bugzilla web interface).
> >
> > On Tue, 25 Mar 2008 15:11:15 -0700 (PDT)
> > bugme-daemon@xxxxxxxxxxxxxxxxxxx wrote:
> >
> > > http://bugzilla.kernel.org/show_bug.cgi?id=10328
> > >
> > >            Summary: [regression] performance drop for glx
> > >
> > > after commit 4138cc3418f5eaa7524ff8e927102863f1ba0ea5 i expirience some grafik
> > > related perfomance issues.
> > >
> > > I used glxgears for test.
> > > before this patch: 1281.005 FPS
> > > and after: 765.000 FPS
> > It nearly halved.
> >
> > > latest tested commit a4083c9271e0a697278e089f2c0b9a95363ada0a
> > > still hase bad performance.
> > >
> > > I use Pentium D with 2GB RAM, Grafick: i945G, ICH7
> > That's 
> >
> > : commit 4138cc3418f5eaa7524ff8e927102863f1ba0ea5
> > : Author: Siddha, Suresh B <suresh.b.siddha@xxxxxxxxx>
> > : Date:   Wed Jan 30 13:33:43 2008 +0100
> > : 
> > :     x86: set strong uncacheable where UC is really desired
> > :     
> > :     Also use _PAGE_PWT for all the mappings which need uncache mapping.
> > :     Instead of existing PAT2 which is UC- (and can be overwritten by MTRRs),
> > :     we now use PAT3 which is strong uncacheable.
> > :     
> > :     This makes it consistent with pgprot_noncached()
>
> Alexey, Can you please try the appended patch?
>
> Andrew, can you please push the appended patch for 2.6.25? Thanks.
> ---
>
> fb drivers are using ioremap()/ioremap_nocache(), followed by mtrr_add with
> WC attribute. Recent changes in page attribute code made both
> ioremap()/ioremap_nocache() mappings as UC (instead of previous UC-). This
> breaks the graphics performance, as the effective memory type is UC instead
> of expected WC.
>
> The correct way to fix this is to add ioremap_wc() (which uses UC- in the
> absence of PAT kernel support and WC with PAT) and change all the
> fb drivers to use this new ioremap_wc() API.
>
> We can take this correct and longer route for post 2.6.25. For now,
> revert back to the UC- behavior for ioremap/ioremap_nocache.

I would still like to add an ioremap_wc() even in 2.6.25; even if it's for now
identical to ioremap_nocache(). Better get the right API in place as soon as possible

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