netdev - Re: [Intel-wired-lan] Small Integers: Big Penalty

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Message-ID: <Zyiu9phq8/EchHxd@mev-dev.igk.intel.com>
Date: Mon, 4 Nov 2024 12:24:38 +0100
From: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
To: Paul Menzel <pmenzel@...gen.mpg.de>
Cc: David Laight <David.Laight@...lab.com>, wojciech.drewek@...el.com,
	marcin.szycik@...el.com, netdev@...r.kernel.org,
	konrad.knitter@...el.com, pawel.chmielewski@...el.com,
	horms@...nel.org, intel-wired-lan@...ts.osuosl.org,
	pio.raczynski@...il.com, sridhar.samudrala@...el.com,
	jacob.e.keller@...el.com, jiri@...nulli.us,
	przemyslaw.kitszel@...el.com
Subject: Re: [Intel-wired-lan] Small Integers: Big Penalty

On Mon, Nov 04, 2024 at 10:12:14AM +0100, Paul Menzel wrote:
> [Cc: -nex.sw.ncis.nat.hpm.dev@...el.com (550 #5.1.0 Address rejected.)]
> 
> Am 04.11.24 um 10:09 schrieb Paul Menzel:
> > Dear David, dear Michal,
> > 
> > 
> > Am 04.11.24 um 09:51 schrieb David Laight:
> > > From: Michal Swiatkowski
> > > > Sent: 04 November 2024 07:03
> > > ...
> > > > > The type of the devlink parameters msix_vec_per_pf_{min,max} is
> > > > > specified as u32, so you must use value.vu32 everywhere you work with
> > > > > them, not vu16.
> > > > > 
> > > > 
> > > > I will change it.
> > > 
> > > You also need a pretty good reason to use u16 anywhere at all.
> > > Just because the domain of the value is small doesn't mean the
> > > best type isn't [unsigned] int.
> > > 
> > > Any arithmetic (particularly on non x86) is likely to increase
> > > the code size above any perceived data saving.
> > 
> > In 2012 Scott Duplichan wrote *Small Integers: Big Penalty* [1]. Of
> > course you always should measure yourself.
> > 

Yeah, I chose it, because previously it was stored in u16. I will change
it to u32 too, as it is stored in structure that doesn't really need to
be small.

Thanks for comments and link to the article.
Michal

> > 
> > Kind regards,
> > 
> > Paul
> > 
> > 
> > [1]: https://notabs.org/coding/smallIntsBigPenalty.htm