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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
parentadf52235b4082e67f31bf1fba36f1dce312633d6 (diff)
downloadop-kernel-dev-b5c9ff731f3cee5a2f2d7154f48f8006b48eb66d.zip
op-kernel-dev-b5c9ff731f3cee5a2f2d7154f48f8006b48eb66d.tar.gz
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>
-rw-r--r--arch/x86/include/asm/kvm_emulate.h5
-rw-r--r--arch/x86/kvm/x86.c17
2 files changed, 18 insertions, 4 deletions
diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index ab09ba2..c0f77e0 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;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ae2353c..d88de56 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4506,6 +4506,20 @@ static void inject_emulated_exception(struct kvm_vcpu *vcpu)
kvm_queue_exception(vcpu, ctxt->exception.vector);
}
+static void init_decode_cache(struct decode_cache *c,
+ const unsigned long *regs)
+{
+ memset(c, 0, offsetof(struct decode_cache, regs));
+ memcpy(c->regs, regs, sizeof(c->regs));
+
+ c->fetch.start = 0;
+ c->fetch.end = 0;
+ c->io_read.pos = 0;
+ c->io_read.end = 0;
+ c->mem_read.pos = 0;
+ c->mem_read.end = 0;
+}
+
static void init_emulate_ctxt(struct kvm_vcpu *vcpu)
{
struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
@@ -4531,8 +4545,7 @@ static void init_emulate_ctxt(struct kvm_vcpu *vcpu)
X86EMUL_MODE_PROT16;
ctxt->guest_mode = is_guest_mode(vcpu);
- memset(c, 0, sizeof(struct decode_cache));
- memcpy(c->regs, vcpu->arch.regs, sizeof c->regs);
+ init_decode_cache(c, vcpu->arch.regs);
vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
}
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