Re: [PATCH 27/54] lib/bitmap: add bitmap_weight_{cmp, eq, gt, ge, lt, le} functions

[Vaittinen, Matti]

On 1/23/22 20:38, Yury Norov wrote:
> Many kernel users use bitmap_weight() to compare the result against
> some number or expression:
> 
> 	if (bitmap_weight(...) > 1)
> 		do_something();
> 
> It works OK, but may be significantly improved for large bitmaps: if
> first few words count set bits to a number greater than given, we can
> stop counting and immediately return.
> 
> The same idea would work in other direction: if we know that the number
> of set bits that we counted so far is small enough, so that it would be
> smaller than required number even if all bits of the rest of the bitmap
> are set, we can stop counting earlier.
> 
> This patch adds new bitmap_weight_cmp() as suggested by Michał Mirosław
> and a family of eq, gt, ge, lt and le wrappers to allow this optimization.
> The following patches apply new functions where appropriate.
> 

Thanks for pushing this improvement Yury. Seeing how much this has 
evolved from the single_bit_set() suggestion - it'd be a bit thick from 
me to add a suggested-by ;) I did review it though and it looks good to me!

Reviewed-by: Matti Vaittinen <matti.vaittinen@xxxxxxxxxxxxxxxxx>

> Suggested-by: "Michał Mirosław" <mirq-linux@xxxxxxxxxxxx> (for bitmap_weight_cmp)
> Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
> ---
>   include/linux/bitmap.h | 80 ++++++++++++++++++++++++++++++++++++++++++
>   lib/bitmap.c           | 21 +++++++++++
>   2 files changed, 101 insertions(+)


-- 
The Linux Kernel guy at ROHM Semiconductors

Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
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90220 OULU
FINLAND

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