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

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Date:	Sat, 20 Feb 2016 14:51:36 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	Pavel Machek <pavel@....cz>
Cc:	kernel list <linux-kernel@...r.kernel.org>, axboe@...com,
	hch@....de
Subject: Re: 4.4-final: 28 bioset threads on small notebook

On Sat, Feb 20 2016 at  1:42pm -0500,
Pavel Machek <pavel@....cz> wrote:

> On Sat 2016-02-20 18:40:35, Pavel Machek wrote:
> > 
> > On Fri 2015-12-11 09:08:41, Mike Snitzer wrote:
> > > On Fri, Dec 11 2015 at  5:49am -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 :-(.
> 									Pavel

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).

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).