linux-kernel - Re: [PATCH v2] minmax: clamp more efficiently by avoiding extra comparison

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Message-Id: <20220923155412.b0132fc62eca18817a023cd2@linux-foundation.org>
Date:   Fri, 23 Sep 2022 15:54:12 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] minmax: clamp more efficiently by avoiding extra
 comparison

On Fri, 23 Sep 2022 17:40:01 +0200 "Jason A. Donenfeld" <Jason@...c4.com> wrote:

> Currently the clamp algorithm does:
> 
> 	if (val > hi)
> 		val = hi;
> 	if (val < lo)
> 		val = lo;
> 
> But since hi > lo by definition, this can be made more efficient with:
> 
> 	if (val > hi)
> 		val = hi;
> 	else if (val < lo)
> 		val = lo;
> 
> So fix up the clamp and clamp_t functions to do this, adding the same
> argument checking as for min and min_t.
> 

The patch adds 140 bytes of text to mm/memblock.o, for example. 
Presumably from the additional branch.  Larger text means larger cache
footprint means slower.

So where's the proof that this change gives us a more efficient kernel?