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Subject: Re: [PATCH 1/3] softirq: Use ffs in __do_softirq
From: Joe Perches <joe@perches.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Date: Mon, 09 Dec 2013 10:56:46 -0800
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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...