Re: [Xen-devel] [PATCH v5 2/5] x86/hpet: Use singe apic vector rather than irq_descs for HPET interrupts

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.03.14 at 15:40, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 06/03/14 14:33, Jan Beulich wrote:
>>>>> On 05.03.14 at 16:43, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>>>  ** Failing all else, a CPU shall retry to find a free HPET.  This 
>>> guarantees
>>>     that a CPU will never leave hpet_broadcast_enter() without arranging an
>>>     interrupt.
>> For how long? Indefinitely (i.e. until the wakeup time is reached)?
>>
>> All without having looked at the details of the patch yet.
> 
> Forever.  There are certain sleep paths which cannot be aborted by this
> point, so exiting without having set up a wakup is not an option.
> 
> A different option would be to make all sleep paths abortable, at which
> point my v4 series would be appropriate (plus spinlock bugfix)

Or simply always force another channel to an earlier wakeup.

But then again - how would we get into that state in the first
place? There can't be neither late nor early channels. If this is
really just to cope with possible races (which the description
didn't say), then I think I'm fine with the abstract approach.

Jan


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