linux-kernel - Re: [PATCH] Reduce the number of expensive division instructions done by _parse

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Message-ID: <CACVxJT9Z5On2hzZ68qVuj1XM79UzM_ECN81e34p0Y0+V9CLU_w@mail.gmail.com>
Date:	Fri, 10 Feb 2012 15:50:02 +0200
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Howells <dhowells@...hat.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Reduce the number of expensive division instructions done
 by _parse_integer()

On Thu, Feb 9, 2012 at 10:14 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:

Ugh, I'm late to the party.

> Because quite frankly, I think we only support bases 8/10/16 in the
> kernel, and if you really have some case where this all is expensive,
> it might be better to simply have three different functions for the
> three bases. That would turn the multiplies into constants too, and
> also simplify the character tests.

base 2 is used to sort of autolimit input to 0/1 characters.

> That said, I can't really see how this could ever be all that hot a
> function. Did you ever see it in a profile, or was this all just from
> looking at the code?

That's why there was no such check from the beginning -- not
performance critical.
We could maintain small table from which digit overflow can happen,
but since this is already committed...

There is CONFIG_TEST_KSTRTOX, does it still passes?
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