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

Suresh Siddha
2008-03-26T00:42:45Z

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@bugzilla.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@intel.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.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
---

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 4afaba0..794895c 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -137,7 +137,11 @@ static void __iomem *__ioremap(resource_size_t phys_addr, unsigned long size,
switch (mode) {
case IOR_MODE_UNCACHED:
default:
- prot = PAGE_KERNEL_NOCACHE;
+ /*
+ * FIXME: we will use UC MINUS for now, as video fb drivers
+ * depend on it. Upcoming ioremap_wc() will fix this behavior.
+ */
+ prot = PAGE_KERNEL_UC_MINUS;
break;
case IOR_MODE_CACHED:
prot = PAGE_KERNEL;
diff --git a/include/asm-x86/pgtable.h b/include/asm-x86/pgtable.h
index 174b877..9cf472a 100644
--- a/include/asm-x86/pgtable.h
+++ b/include/asm-x86/pgtable.h
@@ -85,6 +85,7 @@ extern pteval_t __PAGE_KERNEL, __PAGE_KERNEL_EXEC;
#define __PAGE_KERNEL_RX (__PAGE_KERNEL_EXEC & ~_PAGE_RW)
#define __PAGE_KERNEL_EXEC_NOCACHE (__PAGE_KERNEL_EXEC | _PAGE_PCD | _PAGE_PWT)
#define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_PCD | _PAGE_PWT)
+#define __PAGE_KERNEL_UC_MINUS (__PAGE_KERNEL | _PAGE_PCD)
#define __PAGE_KERNEL_VSYSCALL (__PAGE_KERNEL_RX | _PAGE_USER)
#define __PAGE_KERNEL_VSYSCALL_NOCACHE (__PAGE_KERNEL_VSYSCALL | _PAGE_PCD | _PAGE_PWT)
#define __PAGE_KERNEL_LARGE (__PAGE_KERNEL | _PAGE_PSE)
@@ -101,6 +102,7 @@ extern pteval_t __PAGE_KERNEL, __PAGE_KERNEL_EXEC;
#define PAGE_KERNEL_EXEC MAKE_GLOBAL(__PAGE_KERNEL_EXEC)
#define PAGE_KERNEL_RX MAKE_GLOBAL(__PAGE_KERNEL_RX)
#define PAGE_KERNEL_NOCACHE MAKE_GLOBAL(__PAGE_KERNEL_NOCACHE)
+#define PAGE_KERNEL_UC_MINUS MAKE_GLOBAL(__PAGE_KERNEL_UC_MINUS)
#define PAGE_KERNEL_EXEC_NOCACHE MAKE_GLOBAL(__PAGE_KERNEL_EXEC_NOCACHE)
#define PAGE_KERNEL_LARGE MAKE_GLOBAL(__PAGE_KERNEL_LARGE)
#define PAGE_KERNEL_LARGE_EXEC MAKE_GLOBAL(__PAGE_KERNEL_LARGE_EXEC)