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

[Jan Kara <jack@suse.cz>]

On Wed 06-01-21 18:02:03, Paolo Valente wrote:
> > Il giorno 5 gen 2021, alle ore 17:29, Jens Axboe <axboe@kernel.dk> ha scritto:
> > 
> > On 1/5/21 9:21 AM, Jan Kara wrote:
> >> On Thu 10-12-20 10:44:33, Jan Kara wrote:
> >>> BFQ computes number of tags it allows to be allocated for each request type
> >>> based on tag bitmap. However it uses 1 << bitmap.shift as number of
> >>> available tags which is wrong. 'shift' is just an internal bitmap value
> >>> containing logarithm of how many bits bitmap uses in each bitmap word.
> >>> Thus number of tags allowed for some request types can be far to low.
> >>> Use proper bitmap.depth which has the number of tags instead.
> >>> 
> >>> Signed-off-by: Jan Kara <jack@suse.cz>
> >> 
> >> Ping Jens? I think it has fallen through the cracks?
> > 
> > More like waiting for Paolo to take a look. Don't mind taking it, and
> > I'll do that now, but I do expect him to review any BFQ patches being
> > sent out.
> 
> Sorry for the delay Jan.  As you know, my priority is currently to
> finalize the patches I have developed with your help; and
> unfortunately I'm way behind.  This is delaying also my review
> activity.
> 
> As for your proposal, I remember I found the right parameter rather
> empirically.  In particular, I seem to remember that the bitmap.depth
> parameter did not contain the value I needed, i.e, it did not
> contain the total number of tags.  But maybe something has changed in
> the meantime.  At any rate, if bitmap.depth does contain that value,
> then your replacement is ok.

Yes, bitmap.depth is the total number of tags AFAIK.

> If your replacement is ok, then I guess you may want to also fix the
> comments above the changes you propose.

Oh right, there's one paragraph in the comment that my patch made
redundant. I'll send a cleanup. Thanks for noticing.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR