linux-kernel - Re: [PATCH] lib/int_sqrt.c: optimize for small argument values

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Message-ID: <20171020162227.GE6524@worktop.programming.kicks-ass.net>
Date:   Fri, 20 Oct 2017 18:22:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Joe Perches <joe@...ches.com>, Michael Davidson <md@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        David Miller <davem@...emloft.net>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib/int_sqrt.c: optimize for small argument values

On Fri, Oct 20, 2017 at 07:18:51AM -0700, Kees Cook wrote:
> On Thu, Oct 19, 2017 at 11:13 PM, Joe Perches <joe@...ches.com> wrote:
> > On Thu, 2017-10-19 at 13:31 -0700, Michael Davidson wrote:
> >> int_sqrt() currently takes approximately constant time
> >> regardless of the value of the argument. By using the
> >> magnitude of the operand to set the initial conditions
> >> for the calculation the cost becomes proportional to
> >> log2 of the argument with the worst case behavior not
> >> being measurably slower than it currently is.
> >
> > https://lkml.org/lkml/2017/7/24/408
> 
> Ah! Cool. I don't see this version queued up for -next. Where does
> Peter's version stand?

Oh, crud, forgot all about it. I'd have to double check I addressed the
concerns Linus had with my Changelogs, but other than that he seemed to
be OK.