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authorTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>2011-05-25 11:09:38 +0900
committerAvi Kivity <avi@redhat.com>2011-07-12 11:45:09 +0300
commitb5c9ff731f3cee5a2f2d7154f48f8006b48eb66d (patch)
treebbea807577dd211bf52eca8397c6630f0bc7a01d /arch/x86/include
parentadf52235b4082e67f31bf1fba36f1dce312633d6 (diff)
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KVM: x86 emulator: Avoid clearing the whole decode_cache
During tracing the emulator, we noticed that init_emulate_ctxt() sometimes took a bit longer time than we expected. This patch is for mitigating the problem by some degree. By looking into the function, we soon notice that it clears the whole decode_cache whose size is about 2.5K bytes now. Furthermore, most of the bytes are taken for the two read_cache arrays, which are used only by a few instructions. Considering the fact that we are not assuming the cache arrays have been cleared when we store actual data, we do not need to clear the arrays: 2K bytes elimination. In addition, we can avoid clearing the fetch_cache and regs arrays. This patch changes the initialization not to clear the arrays. On our 64-bit host, init_emulate_ctxt() becomes 0.3 to 0.5us faster with this patch applied. Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> Cc: Gleb Natapov <gleb@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>
Diffstat (limited to 'arch/x86/include')
-rw-r--r--arch/x86/include/asm/kvm_emulate.h5
1 files changed, 3 insertions, 2 deletions
diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index ab09ba290db..c0f77e09ebc 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -246,8 +246,6 @@ struct decode_cache {
unsigned int d;
int (*execute)(struct x86_emulate_ctxt *ctxt);
int (*check_perm)(struct x86_emulate_ctxt *ctxt);
- unsigned long regs[NR_VCPU_REGS];
- unsigned long eip;
/* modrm */
u8 modrm;
u8 modrm_mod;
@@ -255,6 +253,9 @@ struct decode_cache {
u8 modrm_rm;
u8 modrm_seg;
bool rip_relative;
+ unsigned long eip;
+ /* Fields above regs are cleared together. */
+ unsigned long regs[NR_VCPU_REGS];
struct fetch_cache fetch;
struct read_cache io_read;
struct read_cache mem_read;