Commit de33c442 authored by Suresh Siddha's avatar Suresh Siddha Committed by Ingo Molnar
Browse files

x86 PAT: fix performance drop for glx, use UC minus for ioremap(),... 


x86 PAT: fix performance drop for glx, 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: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent b9b39bfb

arch/x86/mm/ioremap.c

+16 −4
Original line number Diff line number Diff line
@@ -176,11 +176,11 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr, 
		/*

		 * 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_caller(resource_size_t phys_addr, 
	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_caller(resource_size_t phys_addr, 
 */

void __iomem *ioremap_nocache(resource_size_t phys_addr, unsigned long size)

{

	return __ioremap_caller(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_caller(phys_addr, size, val,

				__builtin_return_address(0));

}

EXPORT_SYMBOL(ioremap_nocache);

arch/x86/mm/pageattr.c

+8 −2
Original line number Diff line number Diff line
@@ -777,14 +777,20 @@ 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);

arch/x86/pci/i386.c

+9 −3
Original line number Diff line number Diff line
@@ -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);

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