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Subject[PATCH] [20/36] CPA: Don't flush the caches when the CPU supports self-snoop
Date

When the self-snoop CPUID bit is set change_page_attr() only needs to flush
TLBs, but not the caches.

The description of self-snoop in the Intel manuals is a bit vague
but I got confirmation that this is what SS really means.

This should improve c_p_a() performance significantly on newer
Intel CPUs.

Note: the line > 80 characters will be modified again in a followup
Signed-off-by: Andi Kleen <ak@suse.de>
Acked-by: Jan Beulich <jbeulich@novell.com>

---
arch/x86/mm/pageattr_32.c | 5 +++--
arch/x86/mm/pageattr_64.c | 4 ++--
include/asm-x86/cpufeature.h | 1 +
3 files changed, 6 insertions(+), 4 deletions(-)
Index: linux/arch/x86/mm/pageattr_32.c
===================================================================
--- linux.orig/arch/x86/mm/pageattr_32.c
+++ linux/arch/x86/mm/pageattr_32.c
@@ -97,10 +97,11 @@ static void flush_kernel_map(void *arg)
struct flush_arg *a = (struct flush_arg *)arg;
struct flush *f;

- if ((!cpu_has_clflush || a->full_flush) && boot_cpu_data.x86_model >= 4)
+ if ((!cpu_has_clflush || a->full_flush) && boot_cpu_data.x86_model >= 4 &&
+ !cpu_has_ss)
wbinvd();
list_for_each_entry(f, &a->l, l) {
- if (!a->full_flush)
+ if (!a->full_flush && !cpu_has_ss)
clflush_cache_range((void *)f->addr, PAGE_SIZE);
if (!a->full_flush)
__flush_tlb_one(f->addr);
Index: linux/include/asm-x86/cpufeature.h
===================================================================
--- linux.orig/include/asm-x86/cpufeature.h
+++ linux/include/asm-x86/cpufeature.h
@@ -168,6 +168,7 @@
#define cpu_has_clflush boot_cpu_has(X86_FEATURE_CLFLSH)
#define cpu_has_bts boot_cpu_has(X86_FEATURE_BTS)
#define cpu_has_pat boot_cpu_has(X86_FEATURE_PAT)
+#define cpu_has_ss boot_cpu_has(X86_FEATURE_SELFSNOOP)

#if defined(CONFIG_X86_INVLPG) || defined(CONFIG_X86_64)
# define cpu_has_invlpg 1
Index: linux/arch/x86/mm/pageattr_64.c
===================================================================
--- linux.orig/arch/x86/mm/pageattr_64.c
+++ linux/arch/x86/mm/pageattr_64.c
@@ -94,10 +94,10 @@ static void flush_kernel_map(void *arg)

/* When clflush is available always use it because it is
much cheaper than WBINVD. */
- if (a->full_flush || !cpu_has_clflush)
+ if ((a->full_flush || !cpu_has_clflush) && !cpu_has_ss)
asm volatile("wbinvd" ::: "memory");
list_for_each_entry(f, &a->l, l) {
- if (!a->full_flush)
+ if (!a->full_flush && !cpu_has_ss)
clflush_cache_range((void *)f->addr, PAGE_SIZE);
if (!a->full_flush)
__flush_tlb_one(f->addr);

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