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

Suresh Siddha
2008-04-26T00:07:34Z

On Fri, Apr 25, 2008 at 07:35:23AM +0200, Alexey Fisher wrote:
> > >> 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
> > >
> > > Alexey, Can you please try the appended patch?
> > >
> > > Andrew, can you please push the appended patch for 2.6.25? Thanks.
> > > ---
> > >
>
>
> This issue come again with commit:
>
> commit 2e5d9c857d4e6c9e7b7d8c8c86a68a7842d213d6
> Author: venkatesh.pallipadi@intel.com <venkatesh.pallipadi@intel.com>
> Date: Tue Mar 18 17:00:14 2008 -0700
>
> x86: PAT infrastructure patch
>
> Sets up pat_init() infrastructure.
>

Alexey, Sorry. I missed posting a fix in the post PAT series for this issue. Can you
please try the appended patch and Ack?

copying X folks get their attention and their Ack on the patch and next steps outlined.

Thanks.
---

[patch] use UC minus for ioremap(), ioremap_nocache() and pci_mmap_page_range()

Use UC_MINUS for ioremap(), ioremap_nocache() instead of strong UC.
Once all the X drivers move to ioremap_wc(), we can go back to strong
UC semantics for ioremap() and ioremap_nocache().

To avoid attribute aliasing issues, pci_mmap_page_range() will also
use UC_MINUS for default non write-combining mapping request.

Next steps:
a) change all the video drivers using ioremap() or ioremap_nocache()
and adding WC MTTR using mttr_add() to ioremap_wc()

b) for strict usage, we can go back to strong uc semantics
for ioremap() and ioremap_nocache() after some grace period for
completing step-a.

c) user level X server needs to use the appropriate method for setting
up WC mapping (like using resourceX_wc sysfs file instead of
adding MTRR for WC and using /dev/mem or resourceX under /sys)

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
---

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 3a4baf9..c053977 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -176,11 +176,11 @@ static void __iomem *__ioremap(resource_size_t phys_addr, unsigned long size,
/*
* Do not fallback to certain memory types with certain
* requested type:
- * - request is uncached, return cannot be write-back
- * - request is uncached, return cannot be write-combine
+ * - request is uc-, return cannot be write-back
+ * - request is uc-, return cannot be write-combine
* - request is write-combine, return cannot be write-back
*/
- if ((prot_val == _PAGE_CACHE_UC &&
+ if ((prot_val == _PAGE_CACHE_UC_MINUS &&
(new_prot_val == _PAGE_CACHE_WB ||
new_prot_val == _PAGE_CACHE_WC)) ||
(prot_val == _PAGE_CACHE_WC &&
@@ -201,6 +201,9 @@ static void __iomem *__ioremap(resource_size_t phys_addr, unsigned long size,
default:
prot = PAGE_KERNEL_NOCACHE;
break;
+ case _PAGE_CACHE_UC_MINUS:
+ prot = PAGE_KERNEL_UC_MINUS;
+ break;
case _PAGE_CACHE_WC:
prot = PAGE_KERNEL_WC;
break;
@@ -255,7 +258,16 @@ static void __iomem *__ioremap(resource_size_t phys_addr, unsigned long size,
*/
void __iomem *ioremap_nocache(resource_size_t phys_addr, unsigned long size)
{
- return __ioremap(phys_addr, size, _PAGE_CACHE_UC);
+ /*
+ * Ideally, this should be:
+ * pat_wc_enabled ? _PAGE_CACHE_UC : _PAGE_CACHE_UC_MINUS;
+ *
+ * Till we fix all X drivers to use ioremap_wc(), we will use
+ * UC MINUS.
+ */
+ unsigned long val = _PAGE_CACHE_UC_MINUS;
+
+ return __ioremap(phys_addr, size, val);
}
EXPORT_SYMBOL(ioremap_nocache);

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index c29ebd0..ad3202c 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -779,14 +779,20 @@ static inline int change_page_attr_clear(unsigned long addr, int numpages,

int _set_memory_uc(unsigned long addr, int numpages)
{
+ /*
+ * for now UC MINUS. see comments in ioremap_nocache()
+ */
return change_page_attr_set(addr, numpages,
- __pgprot(_PAGE_CACHE_UC));
+ __pgprot(_PAGE_CACHE_UC_MINUS));
}

int set_memory_uc(unsigned long addr, int numpages)
{
+ /*
+ * for now UC MINUS. see comments in ioremap_nocache()
+ */
if (reserve_memtype(addr, addr + numpages * PAGE_SIZE,
- _PAGE_CACHE_UC, NULL))
+ _PAGE_CACHE_UC_MINUS, NULL))
return -EINVAL;

return _set_memory_uc(addr, numpages);
diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index 94f6c73..8af0f0b 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -301,6 +301,13 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
prot = pgprot_val(vma->vm_page_prot);
if (pat_wc_enabled && write_combine)
prot |= _PAGE_CACHE_WC;
+ else if (pat_wc_enabled)
+ /*
+ * ioremap() and ioremap_nocache() defaults to UC MINUS for now.
+ * To avoid attribute conflicts, request UC MINUS here
+ * aswell.
+ */
+ prot |= _PAGE_CACHE_UC_MINUS;
else if (boot_cpu_data.x86 > 3)
prot |= _PAGE_CACHE_UC;

@@ -319,9 +326,8 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
* - request is uncached, return cannot be write-combine
* - request is write-combine, return cannot be write-back
*/
- if ((flags == _PAGE_CACHE_UC &&
- (new_flags == _PAGE_CACHE_WB ||
- new_flags == _PAGE_CACHE_WC)) ||
+ if ((flags == _PAGE_CACHE_UC_MINUS &&
+ (new_flags == _PAGE_CACHE_WB)) ||
(flags == _PAGE_CACHE_WC &&
new_flags == _PAGE_CACHE_WB)) {
free_memtype(addr, addr+len);