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From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Juri Lelli <juri.lelli@gmail.com>,
	tglx@linutronix.de, mingo@redhat.com, rostedt@goodmis.org,
	oleg@redhat.com, fweisbec@gmail.com, darren@dvhart.com,
	johan.eker@ericsson.com, p.faure@akatech.ch,
	linux-kernel@vger.kernel.org, claudio@evidence.eu.com,
	michael@amarulasolutions.com, fchecconi@gmail.com,
	tommaso.cucinotta@sssup.it, nicola.manica@disi.unitn.it,
	luca.abeni@unitn.it, dhaval.giani@gmail.com, hgu1972@gmail.com,
	paulmck@linux.vnet.ibm.com, raistlin@linux.it,
	insop.song@ericsson.com, liming.wang@windriver.com,
	jkacur@redhat.com, harald.gustafsson@ericsson.com,
	vincent.guittot@linaro.org,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 01/16] math128: Introduce various 128bit primitives
Date: Fri, 26 Oct 2012 11:24:21 +0200	[thread overview]
Message-ID: <20121026092421.GB628@gmail.com> (raw)
In-Reply-To: <1351241389.12171.45.camel@twins>


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

> On Thu, 2012-10-25 at 15:26 -0700, Linus Torvalds wrote:
> > it's the *rest* of the "u128" math I really object to. I also wonder
> > about the u64xu64 math case for SCHED_DEADLINE, because I assume that
> > it doesn't actually end up using the 128-bit result in that form, but
> > scales it down again some way? 
> 
> No, it does a compare on two u128, so it doesn't loose any 
> precision. If it were to scale down again and loose precision 
> I'd agree with you that introducing the u128 stuff is 
> pointless.
> 
> The point is (as mentioned in the comments below) overflowing 
> an actual u64 is rare, however since some of this 
> (specifically the dl_{runtime,deadline} parameters) is user 
> specified, we have to assume we will overflow.

So can we control this by restricting the users and avoiding the 
overflow?

A 2^64 result should be a *huge* amount of space already for 
just about anything.

Thanks,

	Ingo

  reply	other threads:[~2012-10-26  9:24 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-10-24 21:53 [RFC][PATCH 00/16] sched: SCHED_DEADLINE v6 Juri Lelli
2012-10-24 21:53 ` [PATCH 01/16] math128: Introduce various 128bit primitives Juri Lelli
2012-10-24 22:48   ` Juri Lelli
2012-10-24 23:18   ` Linus Torvalds
2012-10-25  0:08     ` Steven Rostedt
2012-10-25  0:09       ` Linus Torvalds
2012-10-25 13:47     ` Peter Zijlstra
2012-10-25 14:13       ` Peter Zijlstra
2012-10-25 22:26       ` Linus Torvalds
2012-10-26  8:49         ` Peter Zijlstra
2012-10-26  9:24           ` Ingo Molnar [this message]
2012-10-26  9:35             ` Peter Zijlstra
2012-10-26  9:42               ` Ingo Molnar
2012-10-26  9:54                 ` Peter Zijlstra
2012-10-26 10:04                   ` Ingo Molnar
2012-10-26 10:36                   ` Thomas Gleixner
2012-10-26 10:44                     ` Peter Zijlstra
2012-10-26 11:11                       ` Ingo Molnar
2012-10-26 12:56                       ` Peter Zijlstra
2012-10-26 18:12                         ` Juri Lelli
2012-10-26 18:28                           ` Steven Rostedt
2012-10-26 18:34                             ` Thomas Gleixner
2012-10-26 18:41                             ` Juri Lelli
2012-10-26 12:39                     ` Steven Rostedt
2012-10-26 13:09                       ` Steven Rostedt
2012-10-26  9:52               ` Harald Gustafsson
2012-10-26 15:17           ` Linus Torvalds
2012-10-25  5:21   ` Geert Uytterhoeven
2012-10-25 13:38     ` Peter Zijlstra
2012-10-24 21:53 ` [PATCH 02/16] math128, x86_64: Implement {mul,add}_u128 in 64bit asm Juri Lelli
2012-10-24 22:27   ` H. Peter Anvin
2012-10-24 22:47     ` Juri Lelli
2012-10-24 22:51       ` H. Peter Anvin
2012-10-24 21:53 ` [PATCH 03/16] sched: add sched_class->task_dead Juri Lelli
2012-10-24 21:53 ` [PATCH 04/16] sched: add extended scheduling interface Juri Lelli
2012-10-24 21:53 ` [PATCH 05/16] sched: SCHED_DEADLINE structures & implementation Juri Lelli
2012-10-24 21:53 ` [PATCH 06/16] sched: SCHED_DEADLINE SMP-related data structures & logic Juri Lelli
2012-10-24 21:53 ` [PATCH 07/16] sched: SCHED_DEADLINE avg_update accounting Juri Lelli
2012-10-24 21:53 ` [PATCH 08/16] sched: add period support for -deadline tasks Juri Lelli
2012-10-24 21:53 ` [PATCH 09/16] sched: add schedstats " Juri Lelli
2012-10-24 21:53 ` [PATCH 10/16] sched: add latency tracing " Juri Lelli
2012-10-24 21:53 ` [PATCH 11/16] rtmutex: turn the plist into an rb-tree Juri Lelli
2012-10-24 21:53 ` [PATCH 12/16] sched: drafted deadline inheritance logic Juri Lelli
2012-10-24 21:53 ` [PATCH 13/16] sched: add bandwidth management for sched_dl Juri Lelli
2012-10-24 21:53 ` [PATCH 14/16] sched: make dl_bw a sub-quota of rt_bw Juri Lelli
2012-10-24 21:53 ` [PATCH 15/16] sched: speed up -dl pushes with a push-heap Juri Lelli
2012-10-24 21:53 ` [PATCH 16/16] sched: add sched_dl documentation Juri Lelli
2012-10-25  7:18 ` [RFC][PATCH 00/16] sched: SCHED_DEADLINE v6 Ingo Molnar
2012-10-25  9:53   ` Borislav Petkov
2012-10-25 16:58   ` Juri Lelli

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