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

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Date:	Wed, 26 Mar 2008 10:55:00 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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,
	arjan@...ux.intel.com, bug-track@...her-privat.net
Subject: Re: [Bug 10328] New: [regression] performance drop for glx

On Wed, Mar 26, 2008 at 06:29:11AM +0100, Ingo Molnar wrote:
> 
> * Suresh Siddha <suresh.b.siddha@...el.com> wrote:
> 
> > 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.
> 
> thanks Suresh, applied.

Well, we need to take care of set_memory_uc() aswell, as the previous version
didn't fix Alexey's issue.

Alexey, can you please test and ack this, before Andrew/Ingo can push relevant
bits to their trees. 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
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@...el.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Alexey Fisher <bug-track@...her-privat.net>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...utronix.de>
---

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/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 14e48b5..7b79f6b 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -771,7 +771,7 @@ static inline int change_page_attr_clear(unsigned long addr, int numpages,
 int set_memory_uc(unsigned long addr, int numpages)
 {
 	return change_page_attr_set(addr, numpages,
-				    __pgprot(_PAGE_PCD | _PAGE_PWT));
+				    __pgprot(_PAGE_PCD));
 }
 EXPORT_SYMBOL(set_memory_uc);
 
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)
--
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