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authorPaolo Bonzini <pbonzini@redhat.com>2016-06-20 17:58:29 +0300
committerIngo Molnar <mingo@kernel.org>2016-07-10 14:33:02 +0300
commit2e9d1e150abf88cb63e5d34ca286edbb95b4c53d (patch)
treebf4b565757b68d99719b0ab2669bb5277d2d3508
parent52e31f89cc40c613b22e62108fe12b27433a888e (diff)
downloadlinux-2e9d1e150abf88cb63e5d34ca286edbb95b4c53d.tar.xz
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 <sys/signal.h> #include <time.h> #include <unistd.h> #include <stdio.h> 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 <pbonzini@redhat.com> Reviewed-by: Rik van Riel <riel@redhat.com> Reviewed-by: Andy Lutomirski <luto@kernel.org> Acked-by: Paolo Bonzini <pbonzini@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org>
-rw-r--r--arch/x86/entry/common.c4
-rw-r--r--include/linux/context_tracking.h15
2 files changed, 17 insertions, 2 deletions
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 \
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index d259274238db..d9aef2a0ec8e 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -31,6 +31,19 @@ static inline void user_exit(void)
context_tracking_exit(CONTEXT_USER);
}
+/* Called with interrupts disabled. */
+static inline void user_enter_irqoff(void)
+{
+ if (context_tracking_is_enabled())
+ __context_tracking_enter(CONTEXT_USER);
+
+}
+static inline void user_exit_irqoff(void)
+{
+ if (context_tracking_is_enabled())
+ __context_tracking_exit(CONTEXT_USER);
+}
+
static inline enum ctx_state exception_enter(void)
{
enum ctx_state prev_ctx;
@@ -69,6 +82,8 @@ static inline enum ctx_state ct_state(void)
#else
static inline void user_enter(void) { }
static inline void user_exit(void) { }
+static inline void user_enter_irqoff(void) { }
+static inline void user_exit_irqoff(void) { }
static inline enum ctx_state exception_enter(void) { return 0; }
static inline void exception_exit(enum ctx_state prev_ctx) { }
static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }