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

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Date:	Fri, 26 Oct 2012 13:11:09 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Juri Lelli <juri.lelli@...il.com>, mingo@...hat.com,
	rostedt@...dmis.org, 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


* Peter Zijlstra <peterz@...radead.org> wrote:

> I had hoped the u128 stuff might be elsewise useful, but if we 
> don't want to go there, that's fine.

I think it needs a clearer usecase - and even then the 32-bit 
behavior still looks rather horrible ...

So if we can escape all that with reasonable restrictions then 
that's far better than taking on this kind of overhead for 
32-bit systems. 32-bit still matters, we do the ktime_t 
complications for 32-bit systems and that's for a far smaller 
effect.

[ Would be nice to also stick in a WARN_ONCE() in the key 
  place(s) just in case, to make sure the overflow cannot happen 
  silently in the future. ]

Thanks,

	Ingo
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