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xen-devel
[Xen-devel] Re: [linux-pm] [PATCH 0/3] xen: Use PM/Hibernate events for
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To: |
Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [linux-pm] [PATCH 0/3] xen: Use PM/Hibernate events for save/restore/chkpt |
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From: |
Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx> |
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Date: |
Mon, 21 Feb 2011 17:17:30 +0000 |
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Cc: |
"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Stefano, Pavel Machek <pavel@xxxxxx>, Shriram Rajagopalan <rshriram@xxxxxxxxx>, "linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx" <linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx> |
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Mon, 21 Feb 2011 09:18:22 -0800 |
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On Mon, 2011-02-21 at 16:40 +0000, Alan Stern wrote:
> On Mon, 21 Feb 2011, Ian Campbell wrote:
>
> > On Sun, 2011-02-20 at 07:49 +0000, Pavel Machek wrote:
> > > On Sat 2011-02-19 15:12:35, Shriram Rajagopalan wrote:
> > > > The current implementation of xen guest save/restore/checkpoint
> > > > functionality
> > > > uses PM_SUSPEND and PM_RESUME events. This is not optimal when taking
> > > > checkpoints of a virtual machine (where the suspend hypercall returns
> > > > non-zero, requiring the devices and xenbus to just pickup from where
> > > > they left
> > > > off instead of a complete teardown/reconnect to backend).
> > > >
> > > > The following set of patches modify this implementation to use
> > > > Hibernate style
> > > > control flow (freeze/restore for save/restore and freeze/thaw for
> > > > checkpoint,
> > > > which is merely a cancelled save akin to failed swsusp() ).
> > > >
> > > > These patches are against Ian Campbell's PVHVM tree at
> > > > git://xenbits.xen.org/people/ianc/linux-2.6.git for-stefano/pvhvm
> > > >
> > > > at commit 8a8d1bc753c4e2dda5f2890292d60c67d6ebb573
> > > > kernel version: 2.6.38-rc4
> > >
> > > Series looks ok to me...
> >
> > Thanks Pavel, may we take that as an Acked-by?
> >
> > For my part the Xen side is:
> > Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>
> There's one part of this which could be troublesome. The new code
> generates FREEZE, THAW, and RESTORE events even in kernels where
> CONFIG_HIBERNATION isn't set. In such kernels, drivers are not
> obliged to handle these events correctly.
The dependencies on CONFIG_HIBERNATION which I can see appear to be more
often at the bus level (e.g. in drivers/acpi drivers/pci/pci-driver.c
etc) is that right?
For a PV guest only the Xen PV drivers really matter.
But for a PVHVM guest you are right since there are the emulated "PC"
devices though which could be problematic. There's nothing especially
thrilling in that set of devices although I don't think that invalidates
your point.
> Shouldn't the CONFIG_XEN_SAVE_RESTORE option select CONFIG_HIBERNATION?
> In which case the #ifdef lines in pm_op() wouldn't need to be changed.
I think selecting user-visible symbols is generally frowned upon.
But apart from that I was concerned that tying the Xen functionality
into the hibernation option was a bit odd/artificial. Perhaps it's the
only solution though.
Ian.
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