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

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Message-ID: <4FE3A495.1030008@zytor.com>
Date:	Thu, 21 Jun 2012 15:47:49 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 06/21/2012 03:43 PM, Andrew Morton wrote:
> 
> Regardless of that, we have some head-scratching to do:
> 
> 
> #define UNCORE_PMU_HRTIMER_INTERVAL       (60 * NSEC_PER_SEC)
> 
> and
> 
> #define NSEC_PER_SEC    1000000000L
> 
> and 60 billion doesn't fit in 32 bits.  So do we fix the
> perf_event_intel_uncore.c callsites?  Or do we fix the
> UNCORE_PMU_HRTIMER_INTERVAL definition?  Or do we fix the NSEC_PER_SEC
> definition?
> 
> I'm thinking perhaps the latter.  What *is* the type of a nanosecond in
> Linux?  include/linux/ktime.h is pretty insistent that it is u64.  If
> so, NSEC_PER_SEC should logically have type ULL.  But changing both its
> size and signedness is a pretty big change.

We could change the size only.  The range from 9223372036.854775808 to
18446744073.709551615 seconds (292-584 years) isn't really that significant.

	-hpa
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