Andi Kleen wrote:
On Wednesday 30 May 2007 16:53:41 Anthony Liguori wrote:
Subject: [PATCH][PARAVIRT] Eliminate unnecessary CR3 read in TLB flush
This patch eliminates the CR3 read (which would cause a VM exit) in the TLB
flush path. The patch is based on Ingo Molnar's paravirt series.
This change could be just done generically for the native architecture, couldn't
it?
Sure. It adds a few more cycles onto native though (two memory reads,
and some math). How does the following look?
Regards,
Anthony Liguori
-Andi
Subject: [PATCH] Avoid reading CR3 on TLB flush
From: Anthony Liguori <aliguori@xxxxxxxxxx>
In a virtualized environment, there is significant overhead in reading and
writing control registers. Since we already have the value of CR3 in
current->active_mm->pgd, we can avoid taking the exit on CR3 read when
doing a TLB flush.
Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>
Index: kvm/include/asm-i386/tlbflush.h
===================================================================
--- kvm.orig/include/asm-i386/tlbflush.h 2007-05-30 10:22:48.000000000 -0500
+++ kvm/include/asm-i386/tlbflush.h 2007-05-30 10:22:54.000000000 -0500
@@ -14,13 +14,12 @@
#define __native_flush_tlb() \
do { \
- unsigned int tmpreg; \
+ unsigned int cr3 = __pa(current->active_mm->pgd); \
\
__asm__ __volatile__( \
- "movl %%cr3, %0; \n" \
"movl %0, %%cr3; # flush TLB \n" \
- : "=r" (tmpreg) \
- :: "memory"); \
+ :: "r" (cr3) \
+ : "memory"); \
} while (0)
/*
@@ -29,18 +28,18 @@
*/
#define __native_flush_tlb_global() \
do { \
- unsigned int tmpreg, cr4, cr4_orig; \
+ unsigned int cr3 = __pa(current->active_mm->pgd); \
+ unsigned int cr4, cr4_orig; \
\
__asm__ __volatile__( \
- "movl %%cr4, %2; # turn off PGE \n" \
- "movl %2, %1; \n" \
- "andl %3, %1; \n" \
- "movl %1, %%cr4; \n" \
- "movl %%cr3, %0; \n" \
- "movl %0, %%cr3; # flush TLB \n" \
- "movl %2, %%cr4; # turn PGE back on \n" \
- : "=&r" (tmpreg), "=&r" (cr4), "=&r" (cr4_orig) \
- : "i" (~X86_CR4_PGE) \
+ "movl %%cr4, %1; # turn off PGE \n" \
+ "movl %1, %0; \n" \
+ "andl %2, %0; \n" \
+ "movl %0, %%cr4; \n" \
+ "movl %3, %%cr3; # flush TLB \n" \
+ "movl %1, %%cr4; # turn PGE back on \n" \
+ : "=&r" (cr4), "=&r" (cr4_orig) \
+ : "i" (~X86_CR4_PGE), "r" (cr3) \
: "memory"); \
} while (0)
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