From: Marcelo Tosatti <mtosatti@redhat.com>
Date: Sat, 25 Apr 2015 01:36:14 +0000 (-0300)
Subject: x86: kvmclock: drop rdtsc_barrier()
X-Git-Tag: firefly_0821_release~176^2~1591^2~92
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=a3eb97bd80134ba07864ca00747466c02118aca1;p=firefly-linux-kernel-4.4.55.git

x86: kvmclock: drop rdtsc_barrier()

Drop unnecessary rdtsc_barrier(), as has been determined empirically,
see 057e6a8c660e95c3f4e7162e00e2fee1fc90c50d for details.

Noticed by Andy Lutomirski.

Improves clock_gettime() by approximately 15% on
Intel i7-3520M @ 2.90GHz.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index d6b078e9fa28..628954ceede1 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -86,7 +86,6 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
 	offset = pvclock_get_nsec_offset(src);
 	ret = src->system_time + offset;
 	ret_flags = src->flags;
-	rdtsc_barrier();
 
 	*cycles = ret;
 	*flags = ret_flags;