linux-kernel - Re: [PATCH 29/54] drivers/iio: replace bitmap_weight() with bitmap_weight

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Date:   Sun, 30 Jan 2022 12:54:08 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Yury Norov <yury.norov@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Laight <David.Laight@...lab.com>,
        Joe Perches <joe@...ches.com>, Dennis Zhou <dennis@...nel.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Nicholas Piggin <npiggin@...il.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Alexey Klimov <aklimov@...hat.com>,
        linux-kernel@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        linux-iio@...r.kernel.org
Subject: Re: [PATCH 29/54] drivers/iio: replace bitmap_weight() with
 bitmap_weight_{eq,gt} where appropriate

On Mon, 24 Jan 2022 14:46:43 +0200
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> On Sun, Jan 23, 2022 at 10:39:00AM -0800, Yury Norov wrote:
> > drivers/iio calls bitmap_weight() to compare the weight of bitmap with
> > a given number. We can do it more efficiently with bitmap_weight_{eq, gt}
> > because conditional bitmap_weight may stop traversing the bitmap earlier,
> > as soon as condition is met.  
> 
> ...
> 
> >  		int i, j;
> >  
> >  		for (i = 0, j = 0;
> > -		     i < bitmap_weight(indio_dev->active_scan_mask,
> > -				       indio_dev->masklength);
> > +		     bitmap_weight_gt(indio_dev->active_scan_mask,
> > +				       indio_dev->masklength, i);
> >  		     i++, j++) {
> >  			j = find_next_bit(indio_dev->active_scan_mask,
> >  					  indio_dev->masklength, j);  
> 
> This smells like room for improvement. Have you checked this deeply?
> 

I have no idea what I was smoking that day.
It was near 10 years ago, so I'll blame my younger self ;)

Jonathan