Message-ID: <4FE3A9DF.20303@zytor.com>
Date: Thu, 21 Jun 2012 16:10:23 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andrew Morton <akpm@linux-foundation.org>
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Subject: Re: [tip:perf/core] perf/x86: Add generic Intel uncore PMU support
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On 06/21/2012 03:51 PM, Andrew Morton wrote:
> 
> What *is* significant is the effect of a signedness change upon
> arithmetic, conversions, warnings, etc.  And whether such a change
> might actually introduce bugs.
> 
> 
> Back away and ask the broader questions: why did ktime_t choose
> unsigned?  Is time a signed concept?  What is the right thing to do
> here, from a long-term design perspective?

Time is definitely a signed concept -- it has no beginning or end (well,
the Big Bang, but the ?110 Myr or so uncertainty of the exact timing of
the Big Bang makes it a horridly awkward choice for epoch.)

Now, for some users of time you can inherently guarantee there will
never be any references to time before a particular event, e.g. system
boot, in which case an unsigned number might make sense, but as a whole
I think using a signed type as time_t in nearly all Unix implementation
was The Right Thing.

	-hpa
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