linux-kernel - RE: [PATCH v1 1/8] perf: Increase MAX_NR

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Message-ID: <74f3444d28044d858f0f696cea6485a8@AcuMS.aculab.com>
Date: Mon, 9 Dec 2024 21:35:52 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Ian Rogers' <irogers@...gle.com>, Leo Yan <leo.yan@....com>
CC: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim
	<namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, "Alexander
 Shishkin" <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang
	<kan.liang@...ux.intel.com>, James Clark <james.clark@...aro.org>, Kyle Meyer
	<kyle.meyer@....com>, Ben Gainey <ben.gainey@....com>,
	"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 1/8] perf: Increase MAX_NR_CPUS to 4096

..
> > > Just changing the int to be a s16 would lower the memory overhead,
> > > which is why I'd kind of like the abstraction to be minimal.
> >
> > Here I am not clear what for "changing the int to be a s16".  Could you
> > elaberate a bit for this?
> 
> I meant this :-)
> https://lore.kernel.org/lkml/20241207052133.102829-1-irogers@google.com/

How many time is this allocated?
If it is 2 bytes in a larger structure it is likely to be noise.
For a local the code is likely to be worse.
Any maths and you start forcing the compiler to mask the value
(on pretty much anything except x86).

	David

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