linux-kernel - Re: v4.9, 4.4-final: 28 bioset threads on small notebook, 36 threads on cellphone

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Date:   Wed, 08 Feb 2017 07:57:04 +0100
From:   Mike Galbraith <efault@....de>
To:     Kent Overstreet <kent.overstreet@...il.com>,
        Pavel Machek <pavel@....cz>
Cc:     Mike Snitzer <snitzer@...hat.com>,
        kernel list <linux-kernel@...r.kernel.org>, axboe@...com,
        hch@....de, 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: v4.9, 4.4-final: 28 bioset threads on small notebook, 36
 threads on cellphone

On Tue, 2017-02-07 at 19:58 -0900, Kent Overstreet wrote:
> On Tue, Feb 07, 2017 at 09:39:11PM +0100, Pavel Machek wrote:
> > On Mon 2017-02-06 17:49:06, Kent Overstreet wrote:
> > > On Mon, Feb 06, 2017 at 04:47:24PM -0900, Kent Overstreet wrote:
> > > > On Mon, Feb 06, 2017 at 01:53:09PM +0100, Pavel Machek wrote:
> > > > > Still there on v4.9, 36 threads on nokia n900 cellphone.
> > > > > 
> > > > > So.. what needs to be done there?
> > > 
> > > > But, I just got an idea for how to handle this that might be halfway sane, maybe
> > > > I'll try and come up with a patch...
> > > 
> > > Ok, here's such a patch, only lightly tested:
> > 
> > I guess it would be nice for me to test it... but what it is against?
> > I tried after v4.10-rc5 and linux-next, but got rejects in both cases.
> 
> Sorry, I forgot I had a few other patches in my branch that touch
> mempool/biosets code.
> 
> Also, after thinking about it more and looking at the relevant code, I'm pretty
> sure we don't need rescuer threads for block devices that just split bios - i.e.
> most of them, so I changed my patch to do that.
> 
> Tested it by ripping out the current->bio_list checks/workarounds from the
> bcache code, appears to work:

Patch killed every last one of them, but..

homer:/root # dmesg|grep WARNING
[   11.701447] WARNING: CPU: 4 PID: 801 at block/bio.c:388 bio_alloc_bioset+0x1a7/0x240
[   11.711027] WARNING: CPU: 4 PID: 801 at block/blk-core.c:2013 generic_make_request+0x191/0x1f0
[   19.728989] WARNING: CPU: 0 PID: 717 at block/bio.c:388 bio_alloc_bioset+0x1a7/0x240
[   19.737020] WARNING: CPU: 0 PID: 717 at block/blk-core.c:2013 generic_make_request+0x191/0x1f0
[   19.746173] WARNING: CPU: 0 PID: 717 at block/bio.c:388 bio_alloc_bioset+0x1a7/0x240
[   19.755260] WARNING: CPU: 0 PID: 717 at block/blk-core.c:2013 generic_make_request+0x191/0x1f0
[   19.763837] WARNING: CPU: 0 PID: 717 at block/bio.c:388 bio_alloc_bioset+0x1a7/0x240
[   19.772526] WARNING: CPU: 0 PID: 717 at block/blk-core.c:2013 generic_make_request+0x191/0x1f0