Re: [PATCH] Revert "bfq: Fix computation of shallow depth"

Jens Axboe
2021-02-02T14:39:38Z

On 2/2/21 5:28 AM, Jan Kara wrote:
> Hello!
>
> On Fri 29-01-21 19:18:08, Lin Feng wrote:
>> This reverts commit 6d4d273588378c65915acaf7b2ee74e9dd9c130a.
>>
>> bfq.limit_depth passes word_depths[] as shallow_depth down to sbitmap core
>> sbitmap_get_shallow, which uses just the number to limit the scan depth of
>> each bitmap word, formula:
>> scan_percentage_for_each_word = shallow_depth / (1 << sbimap->shift) * 100%
>
> Looking at sbitmap_get_shallow() again more carefully, I agree that I
> misunderstood how shallow_depth argument gets used and the original code
> was correct and I broke it. Thanks for spotting this!
>
> What I didn't notice is that shallow_depth indeed gets used for each bitmap
> word separately and not for bitmap as a whole. I'd say this could use some
> more documentation but that's unrelated to your revert. So feel free to add:
>
> Reviewed-by: Jan Kara <jack@suse.cz>

I don't have the original patch (neither directly nor in the archive), so
I had to hand-apply it. In any case, applied for 5.11, thanks.

--
Jens Axboe