diff options
| author | Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> | 2011-05-25 11:09:38 +0900 |
|---|---|---|
| committer | Avi Kivity <avi@redhat.com> | 2011-07-12 11:45:09 +0300 |
| commit | b5c9ff731f3cee5a2f2d7154f48f8006b48eb66d (patch) | |
| tree | bbea807577dd211bf52eca8397c6630f0bc7a01d | |
| parent | adf52235b4082e67f31bf1fba36f1dce312633d6 (diff) | |
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.h | 5 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 17 |
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 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; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ae2353c5020..d88de565d0c 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; } |