linux-kernel - Re: [tip:perf/core] perf/x86: Add generic Intel uncore PMU support

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Date:	Thu, 21 Jun 2012 16:29:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, torvalds@...ux-foundation.org,
	zheng.z.yan@...el.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/x86: Add generic Intel uncore PMU support

On Thu, 21 Jun 2012 16:22:50 -0700
"H. Peter Anvin" <hpa@...or.com> wrote:

> On 06/21/2012 04:18 PM, Andrew Morton wrote:
> >>
> >> So why is ktime_t unsigned?
> > 
> > err, actually, it isn't.  But lots of the APIs to manipulate ktime_t
> > use u64.  Reason?
> > 
> > I do agree that time quantities should be signed.
> 
> No idea... probably because when representing an actual wall time since
> the POSIX epoch that can happen during the poweron time on the system,
> the number will be positive since the POSIX epoch predates Linux.
> 

hm.

I'll stick this in my tree and see what happens:

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: include/linux/time.h: make NSEC_PER_SEC 64-bit on 32-bit architectures	

Nanoseconds are usually represented with 64-bit types (s64 and sometimes
u64).  The 32-bit definition of NSEC_PER_SEC can lead to compile-time and
runtime arithmetic overflows on 32-bit systems.

So switch NSEC_PER_SEC to a 64-bit type using "LL".

Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...x.de>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 include/linux/time.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN include/linux/time.h~include-linux-timeh-make-nsec_per_sec-64-bit-on-32-bit-architectures include/linux/time.h
--- a/include/linux/time.h~include-linux-timeh-make-nsec_per_sec-64-bit-on-32-bit-architectures
+++ a/include/linux/time.h
@@ -37,7 +37,7 @@ extern struct timezone sys_tz;
 #define NSEC_PER_USEC	1000L
 #define NSEC_PER_MSEC	1000000L
 #define USEC_PER_SEC	1000000L
-#define NSEC_PER_SEC	1000000000L
+#define NSEC_PER_SEC	1000000000LL
 #define FSEC_PER_SEC	1000000000000000LL
 
 #define TIME_T_MAX	(time_t)((1UL << ((sizeof(time_t) << 3) - 1)) - 1)
_

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