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Date: Wed, 15 Dec 2021 08:40:10 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Yury Norov' <yury.norov@...il.com>,
Michał Mirosław <mirq-linux@...e.qmqm.pl>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"James E.J. Bottomley" <jejb@...ux.ibm.com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Alexey Klimov <aklimov@...hat.com>,
Amitkumar Karwar <amitkarwar@...il.com>,
Andi Kleen <ak@...ux.intel.com>, Andrew Lunn <andrew@...n.ch>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Gross <agross@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
"Andy Shevchenko" <andy@...radead.org>,
Anup Patel <anup.patel@....com>,
"Ard Biesheuvel" <ardb@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
"Catalin Marinas" <catalin.marinas@....com>,
Christoph Hellwig <hch@....de>,
"Christoph Lameter" <cl@...ux.com>,
Daniel Vetter <daniel@...ll.ch>,
Dave Hansen <dave.hansen@...ux.intel.com>,
David Airlie <airlied@...ux.ie>,
Dennis Zhou <dennis@...nel.org>,
Dinh Nguyen <dinguyen@...nel.org>,
Geetha sowjanya <gakula@...vell.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
Guo Ren <guoren@...nel.org>,
Hans de Goede <hdegoede@...hat.com>,
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Ian Rogers <irogers@...gle.com>,
Ingo Molnar <mingo@...hat.com>,
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Lee Jones <lee.jones@...aro.org>,
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Roy Pledge <Roy.Pledge@....com>,
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Saeed Mahameed <saeedm@...dia.com>,
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Solomon Peachy <pizza@...ftnet.org>,
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Thomas Gleixner <tglx@...utronix.de>,
"Ulf Hansson" <ulf.hansson@...aro.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
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<linux-snps-arc@...ts.infradead.org>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: RE: [PATCH 2/9] lib/bitmap: implement bitmap_{empty,full} with
bitmap_weight_eq()
From: Yury Norov
> Sent: 14 December 2021 19:43
...
>
> I think that for long bitmaps the most time consuming operation is moving
> data to L1, and for short bitmaps the difference between approaches is
> barely measurable.
>
> But hweght_long on each iteration can't be more effective than the current
> version. So, I'll drop this patch for v2 and keep things unchanged.
Actually do bitmap_full/empty() calls make any sense at all?
The result is stale since bitmaps are designed to do locked operations.
If you have a lock covering the bitmap then you should be using
something that uses non-locked accesses.
Rightly or wrongly that isn't the bitmap api.
David
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