From: Peter Zijlstra <peterz@infradead.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
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: Thu, 20 Jul 2017 12:10:01 +0200 [thread overview]
Message-ID: <20170720101001.kubsvi5mpzwp3ujd@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1454373398.7627.193.camel@edumazet-glaptop2.roam.corp.google.com>
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")
next prev parent reply other threads:[~2017-07-20 10:10 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-28 21:42 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 [this message]
2017-07-24 13:28 ` Eric Dumazet
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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