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Message-Id: <210a076ea197ae384705d2c02cfff12a951a62f8.1399057218.git.luto@amacapital.net> Date: Fri, 2 May 2014 12:04:12 -0700 From: Andy Lutomirski <luto@...capital.net> To: linux-kernel@...r.kernel.org, x86@...nel.org, "H. Peter Anvin" <h.peter.anvin@...el.com>, Linus Torvalds <torvalds@...ux-foundation.org> Cc: Andy Lutomirski <luto@...capital.net> Subject: [RFC/HACK] x86: Fast return to kernel This speeds up my kernel_pf microbenchmark by about 17%. The cfi annotations need some work. Signed-off-by: Andy Lutomirski <luto@...capital.net> --- My test case is here: https://gitorious.org/linux-test-utils/linux-clock-tests/source/kernel_pf.c This could have some other interesting benefits. For example, pages faults that happen during an NMI might not re-enable NMIs. arch/x86/kernel/entry_64.S | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 1e96c36..922a057 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1033,9 +1033,24 @@ retint_swapgs: /* return to user-space */ retint_restore_args: /* return to kernel space */ DISABLE_INTERRUPTS(CLBR_ANY) /* - * The iretq could re-enable interrupts: + * The popfq could re-enable interrupts: */ TRACE_IRQS_IRETQ + + /* Fast return to kernel. */ + movq RSP-ARGOFFSET(%rsp), %rsi + subq $16, %rsi + movq EFLAGS-ARGOFFSET(%rsp), %rdi + movq %rdi, (%rsi) + movq RIP-ARGOFFSET(%rsp), %rdi + movq %rdi, 8(%rsi) + movq %rsi, RIP-ARGOFFSET(%rsp) + RESTORE_ARGS 1,8,1 + popq %rsp + popfq + /* Interrupts are still off because of the one-insn grace period. */ + retq + restore_args: RESTORE_ARGS 1,8,1 -- 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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