Re: [Xen-devel] [RFC Patch] x86/hpet: Disable interrupts while running hpet interrupt handler.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.08.13 at 15:23, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 06/08/13 12:44, Jan Beulich wrote:
>>>>> On 06.08.13 at 12:32, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>>> The machine we found this crash on is a Dell R310.  4 CPUs, 16G Ram.
>> Not all that big.
>>
>>> The full boot xl dmesg is attached, but it appears that the are 8
>>> broadcast hpets.  This is futher backed up by the 'i' debugkey (also
>>> attached)
>> Right. And with fewer CPUs than HPET channels, you could get
>> the system into a mode where each CPU uses a dedicated channel
>> ("maxcpus=4", suppressing registration of all the disabled ones).
> 
> Does this setup actually mean that there are 8 hpets which are all
> broadcasting to every pcpu?  The affinities listed in debug-keys 'i'
> seem to be towards single pcpus, but the order looks peculiar to say the
> least.

No, each channel will be used for just one CPU when there are at
least as many channels as CPUs. The difference between not using
said command line option and using it is that in the former case a
new channel would get assigned to a CPU each time it needs one,
while in the latter case a static (pre-)assignment is used, i.e. each
CPU will use always the same single channel.

Jan


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