From: "George Spelvin" <linux@horizon.com>
To: hpa@linux.intel.com
Cc: linux-kernel@vger.kernel.org, tytso@mit.edu
Subject: Re: Thought about credit_entropy_bits() math
Date: 21 Oct 2015 14:13:16 -0400 [thread overview]
Message-ID: <20151021181316.25618.qmail@ns.horizon.com> (raw)
In-Reply-To: <5626B01F.9050305@linux.intel.com>
(Resend because I can't spell "kernel.org".)
H. Peter Anvin wrote:
> The main advantage with this approximation is that it doesn't need a
> multiplication instruction. Instead, it can be implemented with two
> shifts and a subtract on hardware for which multiplication is slow.
Er... I'm as addicted to micro-optimization as anyone, which is why
I posted all those various approximations, but I'm taking about going
from one to two, not zero to one.
The current approximaion is used right in the middle of a non-constant
multiply:
unsigned int add = ((pool_size - entropy_count)*anfrac*3) >> s;
(Does Linux even run on any hardware without a multiply instruction?
There are tons of multiplies all over the scheduler. The worst cases
I can think of just have slow bitwise multiplies: the nommu 68000 and
SPARCv7's multiply step.)
parent reply other threads:[~2015-10-21 18:13 UTC|newest]
Thread overview: expand[flat|nested] mbox.gz Atom feed
[parent not found: <5626B01F.9050305@linux.intel.com>]
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