linux-kernel - Re: 4.4-final: 28 bioset threads on small notebook

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Date:	Sat, 20 Feb 2016 15:38:57 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	Pavel Machek <pavel@....cz>
Cc:	kernel list <linux-kernel@...r.kernel.org>, axboe@...com,
	hch@....de, kent.overstreet@...il.com, neilb@...e.de,
	martin.petersen@...cle.com, dpark@...teo.net,
	ming.l@....samsung.com, dm-devel@...hat.com,
	ming.lei@...onical.com, agk@...hat.com, jkosina@...e.cz,
	geoff@...radead.org, jim@...n.com, pjk1939@...ux.vnet.ibm.com,
	minchan@...nel.org, ngupta@...are.org, oleg.drokin@...el.com,
	andreas.dilger@...el.com
Subject: Re: 4.4-final: 28 bioset threads on small notebook

On Sat, Feb 20 2016 at  3:04pm -0500,
Pavel Machek <pavel@....cz> wrote:

> Hi!
> 
> > > > > > I know it is normal to spawn 8 threads for every single function,
> > > > > ...
> > > > > > but 28 threads?
> > > > > > 
> > > > > > root       974  0.0  0.0      0     0 ?        S<   Dec08   0:00 [bioset]
> > > > > ...
> > > > > 
> > > > > How many physical block devices do you have?
> > > > > 
> > > > > DM is doing its part to not contribute to this:
> > > > > dbba42d8a ("dm: eliminate unused "bioset" process for each bio-based DM device")
> > > > > 
> > > > > (but yeah, all these extra 'bioset' threads aren't ideal)
> > > > 
> > > > Still there in 4.4-final.
> > > 
> > > ...and still there in 4.5-rc4 :-(.
> > 
> > You're directing this concern to the wrong person.
> > 
> > I already told you DM is _not_ contributing any extra "bioset" threads
> > (ever since commit dbba42d8a).
> 
> Well, sorry about that. Note that l-k is on the cc list, so hopefully
> the right person sees it too.
> 
> Ok, let me check... it seems that 
> 54efd50bfd873e2dbf784e0b21a8027ba4299a3e is responsible, thus Kent
> Overstreet <kent.overstreet@...il.com> is to blame.
> 
> Um, and you acked the patch, so you are partly responsible.

You still haven't shown you even understand the patch so don't try to
blame me for one aspect you don't like.
 
> > But in general, these "bioset" threads are a side-effect of the
> > late-bio-splitting support.  So is your position on it: "I don't like
> > that feature if it comes at the expense of adding resources I can _see_
> > for something I (naively?) view as useless"?
> 
> > Just seems... naive... but you could be trying to say something else
> > entirely.
> 
> > Anyway, if you don't like something: understand why it is there and then
> > try to fix it to your liking (without compromising why it was there to
> > begin with).
> 
> Well, 28 kernel threads on a notebook is a bug, plain and simple. Do
> you argue it is not?

Just implies you have 28 request_queues right?  You clearly have
something else going on on your notebook than the average notebook user.