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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Andi Kleen <ak@linux.intel.com>, Andi Kleen <andi@firstfloor.org>,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	davidlohr.bueso@hp.com, rafael.j.wysocki@intel.com,
	lenb@kernel.org
Subject: Re: [PATCH] Optimize int_sqrt for small values for faster idle
Date: Mon, 24 Jul 2017 06:28:05 -0700	[thread overview]
Message-ID: <1500902885.12695.0.camel@edumazet-glaptop3.roam.corp.google.com> (raw)
In-Reply-To: <20170720101001.kubsvi5mpzwp3ujd@hirez.programming.kicks-ass.net>

On Thu, 2017-07-20 at 12:10 +0200, Peter Zijlstra wrote:
> On Mon, Feb 01, 2016 at 04:36:38PM -0800, Eric Dumazet wrote:
> > On Tue, 2016-02-02 at 00:08 +0100, Rasmus Villemoes wrote:
> > 
> > > Thanks. (Is there a good way to tell gcc that avg*avg is actually a
> > > 32x32->64 multiplication?)
> > 
> > If avg is 32bit, compiler does that for you.
> > 
> > u32 avg = ...
> > 
> > u64 result = (u64)avg * avg;
> 
> It does not in fact do that :/ See commit:
> 
>   9e3d6223d209 ("math64, timers: Fix 32bit mul_u64_u32_shr() and friends")

Interesting :/

Thanks for letting me know !

  reply	other threads:[~2017-07-24 13:28 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-28 21:42 [PATCH] Optimize int_sqrt for small values for faster idle Andi Kleen
2016-01-28 22:04 ` kbuild test robot
2016-01-28 22:11 ` kbuild test robot
2016-01-28 22:15 ` Joe Perches
2016-01-28 22:40   ` Andi Kleen
2016-01-28 22:22 ` Joe Perches
2016-01-28 22:29 ` Eric Dumazet
2016-01-28 22:30 ` Andi Kleen
2016-01-29  3:59 ` Rafael J. Wysocki
2016-01-31  7:27 ` Thomas Rohwer
2016-02-01 21:25 ` Rasmus Villemoes
2016-02-01 21:36   ` Andi Kleen
2016-02-01 23:08     ` Rasmus Villemoes
2016-02-02  0:00       ` Andi Kleen
2016-02-02  0:36       ` Eric Dumazet
2016-02-02 20:46         ` Rasmus Villemoes
2016-02-02 21:30           ` Eric Dumazet
2017-07-20 10:10         ` Peter Zijlstra
2017-07-24 13:28           ` Eric Dumazet [this message]
2016-02-07 21:32     ` Rasmus Villemoes
2016-02-09 20:44       ` Andi Kleen
2016-02-10 13:31         ` Fengguang Wu

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