linux-kernel - Re: [PATCH RFC - TAKE TWO - 00/12] New version of the BFQ I/O Scheduler

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Date:	Tue, 3 Jun 2014 22:40:57 +0200
From:	Pavel Machek <pavel@....cz>
To:	Paolo Valente <paolo.valente@...more.it>
Cc:	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Li Zefan <lizefan@...wei.com>,
	Fabio Checconi <fchecconi@...il.com>,
	Arianna Avanzini <avanzini.arianna@...il.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org
Subject: Re: [PATCH RFC - TAKE TWO - 00/12] New version of the BFQ I/O
 Scheduler

Hi!

> >>> Well, it's all about how to actually route the changes and in general
> >>> whenever avoidable we try to avoid whole-sale code replacement
> >>> especially when most of the structural code is similar like in this
> >>> case.  Gradually evolving cfq to bfq is likely to take more work but
> >>> I'm very positive that it'd definitely be a lot easier to merge the
> >>> changes that way and people involved, including the developers and
> >>> reviewers, would acquire a lot clearer picture of what's going on in
> >>> the process.  For example, AFAICS, most of the heuristics added by
> >> 
> >> Would it make sense to merge bfq first, _then_ turn cfq into bfq, then
> >> remove bfq?
> >> 
> >> That way
> >> 
> >> 1. Users like me would see improvements soon 
> >> 
> >> 2. BFQ would get more testing early. 
> > 
> > Like this: I applied patch over today's git... 
> > 
> > I only see last bits of panic...
> > 
> > Call trace:
> > __bfq_bfqq_expire
> > bfq_bfqq_expire
> > bfq_dispatch_requests
> > sci_request_fn
> > ...
> > EIP: T.1839+0x26
> > Kernel panic - not syncing: Fatal exception in interrupt
> > Shutting down cpus with NMI
> > 
> > ...
> > 
> > Will retry.
> > 
> > Any ideas?
> > 			

>  We have tried to think about ways to trigger this failure, but in
> vain. Unfortunately, so far no user has reported any failure with
> this last version of bfq either. Finally, we have gone through a new
> static analysis, but also in this case uselessly.

Ok, it is pretty much reproducible here: system just will not finish
booting.

> So, if you are willing to retry, we have put online a version of the code filled with many BUG_ONs. I hope they can make it easier to track down the bug. The archive is here:
> http://algogroup.unimore.it/people/paolo/disk_sched/debugging-patches/3.15.0-rc8-v7rc5.tgz
> 

Ok, let me try.

> Should this attempt be useless as well, I will, if you do not mind, try by asking you more details about your system and reproducing your configuration as much as I can.
> 

It is thinkpad x60 notebook, x86-32 machine with 2GB ram.

But I think it died on my x86-32 core duo desktop, too. 

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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