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2e9d1e150a
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>
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|---|---|---|
| .. | ||
| syscalls | ||
| vdso | ||
| vsyscall | ||
| calling.h | ||
| common.c | ||
| entry_32.S | ||
| entry_64_compat.S | ||
| entry_64.S | ||
| Makefile | ||
| syscall_32.c | ||
| syscall_64.c | ||
| thunk_32.S | ||
| thunk_64.S | ||