linux-kernel - Re: 2.6.25-rc3-mm1 - PROFILE

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Message-ID: <p738x0x5al2.fsf@bingen.suse.de>
Date:	Wed, 05 Mar 2008 18:45:13 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Valdis.Kletnieks@...edu
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.25-rc3-mm1 - PROFILE_LIKELY redux..

Valdis.Kletnieks@...edu writes:
>
> So we're in the same 4K as the VDSO64_* values, but some 0x4fe past the
> gtod_data.  Anybody got a hint as to what the heck it was doing?

Try this patch:

Remove unlikelies in vsyscall path

Remove unlikely in vsyscall path that conflict with unlikely profiling.
The unlikelies shouldn't be needed anyways because gcc predicts
condition leading to early return as unlikely by default and
for the loops it shouldn't make much difference

Signed-off-by: Andi Kleen <ak@...e.de>

Index: linux/arch/x86/kernel/vsyscall_64.c
===================================================================
--- linux.orig/arch/x86/kernel/vsyscall_64.c
+++ linux/arch/x86/kernel/vsyscall_64.c
@@ -128,7 +128,7 @@ static __always_inline void do_vgettimeo
 		seq = read_seqbegin(&__vsyscall_gtod_data.lock);
 
 		vread = __vsyscall_gtod_data.clock.vread;
-		if (unlikely(!__vsyscall_gtod_data.sysctl_enabled || !vread)) {
+		if (!__vsyscall_gtod_data.sysctl_enabled || !vread) {
 			gettimeofday(tv,NULL);
 			return;
 		}
@@ -169,7 +169,7 @@ time_t __vsyscall(1) vtime(time_t *t)
 {
 	struct timeval tv;
 	time_t result;
-	if (unlikely(!__vsyscall_gtod_data.sysctl_enabled))
+	if (!__vsyscall_gtod_data.sysctl_enabled)
 		return time_syscall(t);
 
 	vgettimeofday(&tv, NULL);
Index: linux/arch/x86/vdso/vclock_gettime.c
===================================================================
--- linux.orig/arch/x86/vdso/vclock_gettime.c
+++ linux/arch/x86/vdso/vclock_gettime.c
@@ -48,7 +48,7 @@ static noinline int do_realtime(struct t
 		ts->tv_sec = gtod->wall_time_sec;
 		ts->tv_nsec = gtod->wall_time_nsec;
 		ns = vgetns();
-	} while (unlikely(read_seqretry(&gtod->lock, seq)));
+	} while (read_seqretry(&gtod->lock, seq));
 	timespec_add_ns(ts, ns);
 	return 0;
 }
@@ -77,7 +77,7 @@ static noinline int do_monotonic(struct 
 		ns = gtod->wall_time_nsec + vgetns();
 		secs += gtod->wall_to_monotonic.tv_sec;
 		ns += gtod->wall_to_monotonic.tv_nsec;
-	} while (unlikely(read_seqretry(&gtod->lock, seq)));
+	} while (read_seqretry(&gtod->lock, seq));
 	vset_normalized_timespec(ts, secs, ns);
 	return 0;
 }
@@ -105,7 +105,7 @@ int __vdso_gettimeofday(struct timeval *
 			     sizeof(*tv) != sizeof(struct timespec));
 		do_realtime((struct timespec *)tv);
 		tv->tv_usec /= 1000;
-		if (unlikely(tz != NULL)) {
+		if (tz != NULL) {
 			/* This relies on gcc inlining the memcpy. We'll notice
 			   if it ever fails to do so. */
 			memcpy(tz, &gtod->sys_tz, sizeof(struct timezone));
--
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