Re: [Xen-devel] [PATCH] x86/S3: Fix cpu pool scheduling after suspend/resume

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.04.13 at 15:17, Ben Guthro <benjamin.guthro@xxxxxxxxxx> wrote:
> On Tue, Apr 9, 2013 at 9:03 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 09.04.13 at 14:46, Ben Guthro <benjamin.guthro@xxxxxxxxxx> wrote:
>>> Removing this if condition forces the CPUs to go through the expected
>>> online/offline state, and be properly scheduled after S3.
>>
>> But this doesn't explain _why_ the code block you remove was
>> wrong. And that would be vital to understand, so we can be
>> reasonably sure this change won't lead to regressions elsewhere
>> again.
> 
> I would argue that there has been so many problems with the original
> changeset, that the argument should be in the other direction - since
> this changeset that introduced the system_state variable, nobody has
> been able to successfully suspend, as has been discussed in multiple
> threads over the past year.
> 
> What is the reason that this particular callback gets bailed out of,
> but not others?
> Previously, the code worked, and went through this code path.
> Why this one, in particular?

You'd need to work this out with Juergen and Keir. I don't
really recall the details of the discussion they had back then.

> We have been systematically removing parts of the system_state
> changeset, in regard to the S3 path. This is just another one that
> puts it back to the way it was prior to that changeset (at least the
> second hunk of it)

But as said by Juergen - at the expense of breaking cpupools.

> I'm open to other suggestions, but this was the only path that
> explained the fact that all of the vcpus would end up on cpu0.

Again - one of my main concerns here is that so far I was
under the impression that this "all CPUs on pCPU0" was occurring
sometime, not always. And with that, I would expect the problem
to be a race of some sort, and the fix be dealing with a race.
Which isn't the case.

So the question that first needs answering is - was that impression
of mine wrong? If not, the next question would be whether you
spotted the race...

Jan


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