From: David Howells <dhowells@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: get_order() broken !
Date: Tue, 06 Mar 2007 17:43:16 +0000 [thread overview]
Message-ID: <2793.1173202996@redhat.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0703060910340.5963@woody.linux-foundation.org>
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> Yeah, I think the recent get_order() changes to change it to use ilog2()
> are just crap. I actually looked at it when it went in, but I assumed that
> it had been tested. I don't think it has.
It had, it's just that the testing totally failed to show up the problem; that
and I think my userspace testing went wrong because I made the wrong
assumptions about what the answer should be.
However, having discussed it with Ben, HPA and David Woodhouse and others I've
come up with a patch (sent separately) that should fix it by using:
ilog2((n) - 1) + 1
as the basis for the calculation as this should round up the result. I've
encapsulated this as a function called ilog2_up() and fixed the docs to make
it cleared how ilog2() and co actually work.
David
prev parent reply other threads:[~2007-03-06 17:43 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-06 17:02 get_order() broken ! Benjamin Herrenschmidt
2007-03-06 17:13 ` Linus Torvalds
2007-03-06 17:43 ` David Howells [this message]
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