linux-kernel - Re: long boot delays caused by 070ad7e7 floppy change

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Message-ID: <20120703194047.GN11413@one.firstfloor.org>
Date:	Tue, 3 Jul 2012 21:40:47 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Jiri Kosina <jkosina@...e.cz>,
	Calvin Walton <calvin.walton@...stin.ca>,
	linux-kernel@...r.kernel.org, shemminger@...tta.com
Subject: Re: long boot delays caused by 070ad7e7 floppy change

On Tue, Jul 03, 2012 at 12:12:53PM -0700, Linus Torvalds wrote:
> On Tue, Jul 3, 2012 at 11:58 AM, Andi Kleen <andi@...stfloor.org> wrote:
> >
> > [    2.496493] calling  floppy_init+0x0/0xe46 @ 1
> > [    2.511303] floppy0: lock_fdc: -1 (out of 8)
> > [    2.511346] floppy0: __reschedule_timeout: setting timeout to 750
> 
> Ahhah. And you have CONFIG_HZ250 set, don't you?

Yes I do.

> 
> So it's actually asking for a 3-second timeout like it should.
> 
> > [    2.511372] floppy0: reschedule timeout lock fdc
> > [   22.501757] floppy0: reschedule timeout do wakeup
> 
> But that actual timeout is too damn reliably pretty much exactly 20s
> for it to be anything else.
> 
> I wonder if 'fd_timeout' had been previously queued already with the
> 20s timeout, and not canceled. So then the new queuing of a 3-second
> timeout doesn't actually do anything, because the
> WORK_STRUCT_PENDING_BIT is still set.
> 
> So maybe we're missing a cancel somewhere.
> 
> What happens if you add a
> 
>         cancel_delayed_work(&fd_timeout);
> 
> to before the queue_delayed_work() in __reschedule_timeout()? Does
> that possibly make the delay really be 3 seconds?

That works.  Patch cuts it down to 3s as before 

Tested-by: Andi Kleen <ak@...ux.intel.com>

(and with the async probe patch I posted earlier the kernel
boot time goes down by ~1s from 14 to 13ish)

-Andi

With Linus patch:

[    2.492449] calling  floppy_init+0x0/0xe46 @ 1
[    2.507259] floppy0: lock_fdc: -1 (out of 8)
[    2.507304] floppy0: __reschedule_timeout: setting timeout to 750
[    2.507330] floppy0: reschedule timeout lock fdc
[    5.509642] floppy0: reschedule timeout do wakeup
[    5.509683] floppy0: no floppy controllers found
[    5.509796] initcall floppy_init+0x0/0xe46 returned -19 after 2952148
usecs
[    5.509826] calling  brd_init+0x0/0x1ce @ 1
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