linux-kernel - Re: [PATCH 1/3] softirq: Use ffs in __do

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Message-ID: <1386615406.8168.16.camel@joe-AO722>
Date:	Mon, 09 Dec 2013 10:56:46 -0800
From:	Joe Perches <joe@...ches.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] softirq: Use ffs in __do_softirq

On Mon, 2013-12-09 at 19:44 +0100, Frederic Weisbecker wrote:
> On Sun, Nov 17, 2013 at 01:55:10AM -0800, Joe Perches wrote:
> > Possible speed improvement of the __do_softirq function by using ffs
> > instead of using a while loop with an & 1 test then single bit shift.
[]
> Perhaps using for_each_set_bit() would simplify that more?

It might simplify the appearance of the code but it
would/could expand the amount of generated code because
for_each_set_bit uses an address_of(unsigned long) and
the value tested is an unsigned int.

extra dereferences, can't be in a register, etc...


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