Re: [Xen-devel] [PATCH] xen: use freeze/restore/thaw PM events for suspend/resume/chkpt

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Wed, 2011-02-16 at 18:15 +0000, Shriram Rajagopalan wrote:
> I didnt test the patch against the latest xen_suspend patch series you
> sent out. I couldnt find it in any of the trees. And since you said
> earlier that the xen_hvm_suspend fix would be (re)fixed to PM_FREEZE
> after my patch, I refrained from touching it. But I did test with
> 2.6.38-rc1 32 bit kernel, PVHVM mode. It "seemed" to work fine for
> save/restore/checkpoint. I could see the PM event messages in dmesg
> (freeze, thaw, restore related timing stats)

Great, thanks.

> On a related note, my initial kernel config had somehow enabled
> CONFIG_MICROCODE. 
> So, with a PV kernel (2.6.38-rc1), I got the following WARNING stack
> trace for 
> checkpoint & restore (ie freeze/thaw or freeze/restore)

> [...]

> sysdev_resume() call we make in drivers/xen/manage.c results in
> calling [sysdev_drivers]->(resume)()
> Looking at the microcode_core.c driver, the mc_sysdev resume function 
> raises this warning if more than 1 CPU is online during system resume.

This is known issue, the 1 CPU constraint is a native thing and isn't
applicable to Xen.

There has been a patch floating around for ages. I saw some traffic
about it recently, let me dig...

... aha. it went into -mm last week, see
<201102082204.p18M4bqc028043@xxxxxxxxxxxxxxxxxxxxxxxxxx>

not bad for a patch originally posted in 2009!
http://www.gossamer-threads.com/lists/linux/kernel/1335664

[...]
> Of course, disabling CONFIG_MICROCODE makes the warning go away but I
> was thinking along the lines of a stock kernel config that has lots of
> things enabled. Correct me if I am wrong about this.

Consideration for stock kernel configurations (particularly distro
configs) is absolutely correct, thanks!

Ian.


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