linux-kernel - Re: [PATCH 01/16] math128: Introduce various 128bit primitives

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Date:	Fri, 26 Oct 2012 08:39:15 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Juri Lelli <juri.lelli@...il.com>, mingo@...hat.com,
	oleg@...hat.com, fweisbec@...il.com, darren@...art.com,
	johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fchecconi@...il.com,
	tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...csson.com, liming.wang@...driver.com,
	jkacur@...hat.com, harald.gustafsson@...csson.com,
	vincent.guittot@...aro.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 01/16] math128: Introduce various 128bit primitives

On Fri, 2012-10-26 at 12:36 +0200, Thomas Gleixner wrote:

> By all means. nsec precision is a completly academic thought
> exercise. It's really pointless to even think about anything below
> microseconds resolution.
> 
> We can still have the user space interface handing in the information
> in nsec resolution, but it's reasonable to scale it down to something
> useful. Just shift the incoming information right by 10, so you're in
> the 1us resolution for all the internal math and all your limitation
> problems are gone. A shift by ten for converting back and forth to
> nsecs is not a real performance issue.

Just make sure this is well documented in the man pages, and that should
eliminate any "surprises". This is a new interface, we can just make
this part of the ABI. "The units are in nanoseconds, but all
calculations are performed to the nearest microsecond. Take this into
account for error analysis". People should be fine with this.

-- Steve



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