From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Mark Lord <liml@rtr.ca>, Tejun Heo <tj@kernel.org>
Subject: Re: [git patches] libata hibernation fixes
Date: Tue, 4 Nov 2008 18:07:16 +0100
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Jeff Garzik <jeff@garzik.org>,
       Andrew Morton <akpm@linux-foundation.org>, linux-ide@vger.kernel.org,
       LKML <linux-kernel@vger.kernel.org>
References: <20081104062734.GA4420@havoc.gtf.org> <200811041753.53342.rjw@sisk.pl> <49107F76.60107@rtr.ca>
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On Tuesday, 4 of November 2008, Mark Lord wrote:
> Rafael J. Wysocki wrote:
> > On Tuesday, 4 of November 2008, Linus Torvalds wrote:
> >> On Tue, 4 Nov 2008, Jeff Garzik wrote:
> >>> This adds code at a late stage (heading towards -rc4), but does
> >>> eliminate a particular spin-up overcycling behavior associated with
> >>> hibernation.
> >> What does this have to do with hibernation? 
> >>
> >> If it's a hibernation-only issue, then there is something wrong. 
> > 
> > No, it is not.  On some machines it is a power-off issue, on the others it is
> > hibernation and power-off issue.
> > 
> >> Also, if it is an issue for normal power-off as well, then I wonder why 
> >> this isn't an issue on Windows. Does windows not spin down disks at all?
> > 
> > In fact, AFAICS, it is an issue on Windows as well, at least if
> > other-than-HP-preloaded version of Windows is used.
> > 
> >> IOW, I really don't think this is correct. 
> >>
> >> I _do_ think that correct might be:
> >>
> >>  - maybe we just do something odd and different, triggering some BIOS 
> >>    behavior that isn't there under Windows.
> >>
> >>    So we should power down thigns differently so that the BIOS.
> >>
> >>  - quite possibly: we just should not spin down disks at all, and just 
> >>    flush them and do the "park" command thing. If we're _really_ powering 
> >>    off, the disks will spin down on their own when power goes away. Maybe 
> >>    that's what Windows does?
> >>
> >> So I really don't want to pull this, because I want to get more of an 
> >> explanation for why we need to do this at all. I also don't think this is 
> >> even appropriate at this stage in -rc.
> >>
> >> Is it a regression? If so, that just strengthens the questions above - 
> >> what did _we_ start doing wrong that this is needed at all? Let's just 
> >> stop doing that, not add some idiotic black-list for somethign that _we_ 
> >> do wrong.
> > 
> > This is a regression, but from something like 2.6.25 or even earlier.
> > I think what happened is we started to power-off disks at one point and these
> > BIOS-es just don't like that.
> > 
> > [Note that the issue only appears in _some_ HP boxes, other vendors don't
> > seem to be affected at all.]
> ..
> 
> So, what happens if we just don't ever spin them down from the kernel?
> Presumably they still spin-down normally (HP or otherwise) when the BIOS
> actually cuts the power at the end of all of this?
> 
> Just curious..

Well, I'll let Tejun answer that. :-)

Thanks,
Rafael
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