Re: [Xen-devel] [PATCHv3 3/4] xen: use ticket locks for spin locks

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> David Vrabel <david.vrabel@xxxxxxxxxx> 04/29/15 5:28 PM >>>
>On 29/04/15 00:15, Jan Beulich wrote:
>>>>> David Vrabel <david.vrabel@xxxxxxxxxx> 04/28/15 6:16 PM >>>
>>> Are there any structures whose size you're particularly concerned about?
>> 
>> No specific ones (but of course structures with an inherent size constraint
>> - like struct domain and struct vcpu - are, with all of their sub-structures,
>> primary candidates). I just recall that in some cases (and this may no longer
>> apply due to later additions) structures got arranged specifically taking in
>> mind the 2-byte size of the locks, and the growth here may thus mean a
>> structure size growth of more than just two bytes.
>
>Spin locks are currently 4 bytes (2 bytes for the lock, plus 2 bytes for
>the recurse_{cnt,cpu}), and ticket locks are now 8 bytes (an increase in
>4 bytes).
>
>struct vcpu does not increase in size (there is 56, now 48 bytes, of
>padding before the arch field).
>
>struct domain increases from 3480 to 3544 bytes.

Odd - this suggests there's still some 64-byte alignment somewhere, but I
can't immediately spot it. Only struct vcpu has an obvious 64-byte aligned
field (struct pi_desc) afaics.

Jan


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