x86: fix performance drop for glx

fix the 3D performance drop reported at:

   http://bugzilla.kernel.org/show_bug.cgi?id=10328

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 <[email protected]>
Signed-off-by: Venkatesh Pallipadi <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 4afaba0ed72221175854a856d347179b1ab3e979..794895c6dcc99428b2105a9f4062b109b90f5215 100644 (file)
--- 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 14e48b5a94ba193c1cb4acc667482e05905d373e..7b79f6be4e7df99dc663d2d4c935a7e35f877a3b 100644 (file)
--- 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 174b87738714fe634d135c8738df8a6f5ba8a0c5..9cf472aeb9ce5841185ac52131dc311123c9b6f6 100644 (file)
--- 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)