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

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Date:	Tue, 25 Mar 2008 21:42:23 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	bugme-daemon@...zilla.kernel.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>, venkatesh.pallipadi@...el.com,
	bug-track@...her-privat.net
Subject: Re: [Bug 10328] New: [regression] performance drop for glx

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@...zilla.kernel.org 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@...el.com>
>> : 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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