Re: [Xen-devel] CPU and scheduler init, Part 2

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

That could work, if you want.  ATM I don't allocate anything; if I
need to in the future, I should be able to do it allocation in
alloc_pdata().

I don't strictly need it to run on the processor that's coming up; I just need:
* The function to happen after the cpu ID stuff, so that (for example)
cpu_to_socket() returns a reasonable value
* The function to finish before the cpu tries to run the scheduler

But if you'd rather add CPU_STARTING than an interlock for CPU_ONLINE
for technical reasons, that's fine.

Thanks,
 -George


On Thu, Dec 9, 2010 at 2:16 PM, Keir Fraser <keir@xxxxxxx> wrote:
> On 09/12/2010 12:49, "George Dunlap" <dunlapg@xxxxxxxxx> wrote:
>
>> Keir,
>>
>> I made a cpu status notifier for sched_credit2() to actually read an
>> arrange the runqueue information, and found the next niggle: the
>> callbacks are not guaranteed to finish before the cpu tried to go
>> through the scheduler.  The callback notifiers are handled on the cpu
>> that issues the boot command (i.e., cpu 0 during boot), and there's no
>> interlock to prevent the booted cpu from continuing until the
>> notifiers have completed execution.
>>
>> Making a simple interlock (similar to the one in __cpu_up()) allows
>> the system to boot properly.  Another possibility would be to run the
>> notifiers on the freshly booted cpu before calling into the scheduler,
>> rather than on the cpu that issued the cpu boot sequence.
>
> I could bring Linux's CPU_STARTING notifier over into Xen. Runs in context
> of new CPU before it is fully online (e.g., before interrupts are enabled).
> So you couldn't do any allocations there, or anything else that can fail.
> This might require some juggling to pre-allocate memory (e.g., for
> possibly-required new runqueue) on CPU_UP_PREPARE/alloc_pdata, and
> potentially free that memory if unused on CPU_ONLINE. Or not, if actually
> you require no dynamic memory allocation.
>
> This might be the best solution overall I think? I can knock up a patch for
> CPU_STARTING if that sounds good.
>
>  -- Keir
>
>> Thoughts?
>>
>>  -George
>>
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>
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