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Microoptimize the return path for the fast syscalls on amd64. Arrange

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the code to have the fall-through path to follow the likely target.
Do not use intermediate register to reload user %rsp.

Proposed by:	alc
Reviewed by:	alc, jhb
Approved by:	re (bz)
MFC after:	2 weeks
This commit is contained in:
Konstantin Belousov 2011-09-15 09:53:04 +00:00
parent 073d48133f
commit 7a1c55c380
1 changed files with 10 additions and 10 deletions
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20
sys/amd64/amd64/exception.S
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@ -393,14 +393,8 @@ IDTVEC(fast_syscall)
/* Check for and handle AST's on return to userland. */
movq PCPU(CURTHREAD),%rax
testl $TDF_ASTPENDING | TDF_NEEDRESCHED,TD_FLAGS(%rax)
je 2f
sti
movq %rsp, %rdi
call ast
jmp 1b
.align 16
2: /* Restore preserved registers. */
jne 2f
/* Restore preserved registers. */
MEXITCOUNT
movq TF_RDI(%rsp),%rdi /* bonus; preserve arg 1 */
movq TF_RSI(%rsp),%rsi /* bonus: preserve arg 2 */
@ -408,10 +402,16 @@ IDTVEC(fast_syscall)
movq TF_RAX(%rsp),%rax /* return value 1 */
movq TF_RFLAGS(%rsp),%r11 /* original %rflags */
movq TF_RIP(%rsp),%rcx /* original %rip */
movq TF_RSP(%rsp),%r9 /* user stack pointer */
movq %r9,%rsp /* original %rsp */
movq TF_RSP(%rsp),%rsp /* user stack pointer */
swapgs
sysretq
2: /* AST scheduled. */
sti
movq %rsp,%rdi
call ast
jmp 1b
3: /* Requested full context restore, use doreti for that. */
MEXITCOUNT
jmp doreti