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authorRobin Holt <holt@sgi.com>2010-04-23 19:36:22 +0400
committerH. Peter Anvin <hpa@zytor.com>2010-04-24 02:57:23 +0400
commit1f9cc3cb6a27521edfe0a21abf97d2bb11c4d237 (patch)
treec9af6a71398aed690c1fa813498a0aed8abf2d7b /arch/x86/include/asm/cacheflush.h
parent4daa2a8093ecd1148270a1fc64e99f072b8c2901 (diff)
downloadlinux-1f9cc3cb6a27521edfe0a21abf97d2bb11c4d237.tar.xz
x86, pat: Update the page flags for memtype atomically instead of using memtype_lock
While testing an application using the xpmem (out of kernel) driver, we noticed a significant page fault rate reduction of x86_64 with respect to ia64. For one test running with 32 cpus, one thread per cpu, it took 01:08 for each of the threads to vm_insert_pfn 2GB worth of pages. For the same test running on 256 cpus, one thread per cpu, it took 14:48 to vm_insert_pfn 2 GB worth of pages. The slowdown was tracked to lookup_memtype which acquires the spinlock memtype_lock. This heavily contended lock was slowing down vm_insert_pfn(). With the cmpxchg on page->flags method, both the 32 cpu and 256 cpu cases take approx 00:01.3 seconds to complete. Signed-off-by: Robin Holt <holt@sgi.com> LKML-Reference: <20100423153627.751194346@gulag1.americas.sgi.com> Cc: Venkatesh Pallipadi <venkatesh.pallipadi@gmail.com> Cc: Rafael Wysocki <rjw@novell.com> Reviewed-by: Suresh Siddha <suresh.b.siddha@intel.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/include/asm/cacheflush.h')
-rw-r--r--arch/x86/include/asm/cacheflush.h44
1 files changed, 25 insertions, 19 deletions
diff --git a/arch/x86/include/asm/cacheflush.h b/arch/x86/include/asm/cacheflush.h
index 634c40a739a6..c70068d05f70 100644
--- a/arch/x86/include/asm/cacheflush.h
+++ b/arch/x86/include/asm/cacheflush.h
@@ -44,9 +44,6 @@ static inline void copy_from_user_page(struct vm_area_struct *vma,
memcpy(dst, src, len);
}
-#define PG_WC PG_arch_1
-PAGEFLAG(WC, WC)
-
#ifdef CONFIG_X86_PAT
/*
* X86 PAT uses page flags WC and Uncached together to keep track of
@@ -55,16 +52,24 @@ PAGEFLAG(WC, WC)
* _PAGE_CACHE_UC_MINUS and fourth state where page's memory type has not
* been changed from its default (value of -1 used to denote this).
* Note we do not support _PAGE_CACHE_UC here.
- *
- * Caller must hold memtype_lock for atomicity.
*/
+
+#define _PGMT_DEFAULT 0
+#define _PGMT_WC (1UL << PG_arch_1)
+#define _PGMT_UC_MINUS (1UL << PG_uncached)
+#define _PGMT_WB (1UL << PG_uncached | 1UL << PG_arch_1)
+#define _PGMT_MASK (1UL << PG_uncached | 1UL << PG_arch_1)
+#define _PGMT_CLEAR_MASK (~_PGMT_MASK)
+
static inline unsigned long get_page_memtype(struct page *pg)
{
- if (!PageUncached(pg) && !PageWC(pg))
+ unsigned long pg_flags = pg->flags & _PGMT_MASK;
+
+ if (pg_flags == _PGMT_DEFAULT)
return -1;
- else if (!PageUncached(pg) && PageWC(pg))
+ else if (pg_flags == _PGMT_WC)
return _PAGE_CACHE_WC;
- else if (PageUncached(pg) && !PageWC(pg))
+ else if (pg_flags == _PGMT_UC_MINUS)
return _PAGE_CACHE_UC_MINUS;
else
return _PAGE_CACHE_WB;
@@ -72,25 +77,26 @@ static inline unsigned long get_page_memtype(struct page *pg)
static inline void set_page_memtype(struct page *pg, unsigned long memtype)
{
+ unsigned long memtype_flags = _PGMT_DEFAULT;
+ unsigned long old_flags;
+ unsigned long new_flags;
+
switch (memtype) {
case _PAGE_CACHE_WC:
- ClearPageUncached(pg);
- SetPageWC(pg);
+ memtype_flags = _PGMT_WC;
break;
case _PAGE_CACHE_UC_MINUS:
- SetPageUncached(pg);
- ClearPageWC(pg);
+ memtype_flags = _PGMT_UC_MINUS;
break;
case _PAGE_CACHE_WB:
- SetPageUncached(pg);
- SetPageWC(pg);
- break;
- default:
- case -1:
- ClearPageUncached(pg);
- ClearPageWC(pg);
+ memtype_flags = _PGMT_WB;
break;
}
+
+ do {
+ old_flags = pg->flags;
+ new_flags = (old_flags & _PGMT_CLEAR_MASK) | memtype_flags;
+ } while (cmpxchg(&pg->flags, old_flags, new_flags) != old_flags);
}
#else
static inline unsigned long get_page_memtype(struct page *pg) { return -1; }