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KVM: emulate: avoid per-byte copying in instruction fetches 

We do not need a memory copying loop anymore in insn_fetch; we
can use a byte-aligned pointer to access instruction fields directly
from the fetch_cache.  This eliminates 50-150 cycles (corresponding to
a 5-10% improvement in performance) from each instruction.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2014-05-06 13:05:25 +02:00
parent 5cfc7e0f5e
commit 9506d57de3
1 changed files with 22 additions and 24 deletions
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46
arch/x86/kvm/emulate.c
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@ -708,7 +708,7 @@ static int segmented_read_std(struct x86_emulate_ctxt *ctxt,
* Prefetch the remaining bytes of the instruction without crossing page
* boundary if they are not in fetch_cache yet.
*/
static int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
{
struct fetch_cache *fc = &ctxt->fetch;
int rc;
@ -740,41 +740,39 @@ static int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
return X86EMUL_CONTINUE;
}
static int do_insn_fetch(struct x86_emulate_ctxt *ctxt,
void *__dest, unsigned size)
static __always_inline int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt,
unsigned size)
{
struct fetch_cache *fc = &ctxt->fetch;
u8 *dest = __dest;
u8 *src = &fc->data[ctxt->_eip - fc->start];
/* We have to be careful about overflow! */
if (unlikely(ctxt->_eip > fc->end - size)) {
int rc = do_insn_fetch_bytes(ctxt, size);
if (rc != X86EMUL_CONTINUE)
return rc;
}
while (size--) {
*dest++ = *src++;
ctxt->_eip++;
continue;
}
return X86EMUL_CONTINUE;
if (unlikely(ctxt->_eip > ctxt->fetch.end - size))
return __do_insn_fetch_bytes(ctxt, size);
else
return X86EMUL_CONTINUE;
}
/* Fetch next part of the instruction being emulated. */
#define insn_fetch(_type, _ctxt) \
({ unsigned long _x; \
rc = do_insn_fetch(_ctxt, &_x, sizeof(_type)); \
({ _type _x; \
struct fetch_cache *_fc; \
\
rc = do_insn_fetch_bytes(_ctxt, sizeof(_type)); \
if (rc != X86EMUL_CONTINUE) \
goto done; \
(_type)_x; \
_fc = &ctxt->fetch; \
_x = *(_type __aligned(1) *) &_fc->data[ctxt->_eip - _fc->start]; \
ctxt->_eip += sizeof(_type); \
_x; \
})
#define insn_fetch_arr(_arr, _size, _ctxt) \
({ rc = do_insn_fetch(_ctxt, _arr, (_size)); \
({ \
struct fetch_cache *_fc; \
rc = do_insn_fetch_bytes(_ctxt, _size); \
if (rc != X86EMUL_CONTINUE) \
goto done; \
_fc = &ctxt->fetch; \
memcpy(_arr, &_fc->data[ctxt->_eip - _fc->start], _size); \
ctxt->_eip += (_size); \
})
/*
@ -4236,7 +4234,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
if (insn_len > 0)
memcpy(ctxt->fetch.data, insn, insn_len);
else {
rc = do_insn_fetch_bytes(ctxt, 1);
rc = __do_insn_fetch_bytes(ctxt, 1);
if (rc != X86EMUL_CONTINUE)
return rc;
}