linux-kernel - [PATCH 0/3] lib/int_sqrt: Fix, optimize and document

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Message-Id: <20170724151630.447009076@infradead.org>
Date:   Mon, 24 Jul 2017 17:16:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, akpm@...ux-foundation.org
Cc:     dave@...olabs.net, aksgarg1989@...il.com, tglx@...utronix.de,
        mingo@...nel.org, will.deacon@....com, joe@...ches.com,
        peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/3] lib/int_sqrt: Fix, optimize and document

Hi,

Here are a few patches that should improve things lib/int_sqrt. As stated
elsewhere; I'm looking at using int_sqrt() to calculate the stdev on a normal
distribution and am expecting the input values to be smallish.

In any case, these optimizations should work fine for large numbers too. And
if you have a find-last-set or count-leading-zeros instruction they rock ;-)

I can post the tool used to generate the numbers or do a patch to add it to
tools/testing/ if people care. The cold numbers are fairly sensitive to code
layout (GCC version, random changes etc..), so I expect the branch predictor of
my SKL is only partially confused or there's other things at play. However the
general trend in the numbers seems fairly stable.