From 2e9d1e150abf88cb63e5d34ca286edbb95b4c53d Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 20 Jun 2016 16:58:29 +0200 Subject: x86/entry: Avoid interrupt flag save and restore Thanks to all the work that was done by Andy Lutomirski and others, enter_from_user_mode() and prepare_exit_to_usermode() are now called only with interrupts disabled. Let's provide them a version of user_enter()/user_exit() that skips saving and restoring the interrupt flag. On an AMD-based machine I tested this patch on, with force-enabled context tracking, the speed-up in system calls was 90 clock cycles or 6%, measured with the following simple benchmark: #include #include #include #include unsigned long rdtsc() { unsigned long result; asm volatile("rdtsc; shl $32, %%rdx; mov %%eax, %%eax\n" "or %%rdx, %%rax" : "=a" (result) : : "rdx"); return result; } int main() { unsigned long tsc1, tsc2; int pid = getpid(); int i; tsc1 = rdtsc(); for (i = 0; i < 100000000; i++) kill(pid, SIGWINCH); tsc2 = rdtsc(); printf("%ld\n", tsc2 - tsc1); } Signed-off-by: Paolo Bonzini Reviewed-by: Rik van Riel Reviewed-by: Andy Lutomirski Acked-by: Paolo Bonzini Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kvm@vger.kernel.org Link: http://lkml.kernel.org/r/1466434712-31440-2-git-send-email-pbonzini@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/entry/common.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/x86/entry/common.c') diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index ec138e538c44..618bc61d35b7 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -43,7 +43,7 @@ static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs) __visible void enter_from_user_mode(void) { CT_WARN_ON(ct_state() != CONTEXT_USER); - user_exit(); + user_exit_irqoff(); } #else static inline void enter_from_user_mode(void) {} @@ -274,7 +274,7 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) ti->status &= ~TS_COMPAT; #endif - user_enter(); + user_enter_irqoff(); } #define SYSCALL_EXIT_WORK_FLAGS \ -- cgit v1.2.3 From be8a18e2e98e04a5def5887d913b267865562448 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 20 Jun 2016 16:58:30 +0200 Subject: x86/entry: Inline enter_from_user_mode() This matches what is already done for prepare_exit_to_usermode(), and saves about 60 clock cycles (4% speedup) with the benchmark in the previous commit message. Signed-off-by: Paolo Bonzini Reviewed-by: Rik van Riel Reviewed-by: Andy Lutomirski Acked-by: Paolo Bonzini Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kvm@vger.kernel.org Link: http://lkml.kernel.org/r/1466434712-31440-3-git-send-email-pbonzini@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/entry/common.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/entry/common.c') diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 618bc61d35b7..9e1e27d31c6d 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -40,7 +40,7 @@ static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs) #ifdef CONFIG_CONTEXT_TRACKING /* Called on entry from user mode with IRQs off. */ -__visible void enter_from_user_mode(void) +__visible inline void enter_from_user_mode(void) { CT_WARN_ON(ct_state() != CONTEXT_USER); user_exit_irqoff(); -- cgit v1.2.3