Re: [Xen-devel] [PATCHv6 1/3] xen: use ticket locks for spin locks

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.05.15 at 12:27, <david.vrabel@xxxxxxxxxx> wrote:
> On 18/05/15 16:49, Jan Beulich wrote:
>>>>> On 18.05.15 at 17:33, <david.vrabel@xxxxxxxxxx> wrote:
>>> On 18/05/15 11:16, Jan Beulich wrote:
>>>>>>> On 14.05.15 at 13:21, <david.vrabel@xxxxxxxxxx> wrote:
>>>>>  void _spin_lock(spinlock_t *lock)
>>>>>  {
>>>>> +    spinlock_tickets_t tickets = { .tail = 1, };
>>>>
>>>> This breaks the build on gcc 4.3.x (due to tail being a member of an
>>>> unnamed structure member of a union).
>>>
>>> I don't have a gcc that old to hand but isn't the error here that .tail
>>> is part of the structure that isn't the first member of a union?
>> 
>> No, the error is "unknown field 'tail' specified in initializer", and ...
>> 
>>> Does this fix your gcc 4.3 build?
>> 
>> ... hence this doesn't help. Iirc you just can't have initializers for
>> unnamed fields or their descendants.
> 
> How about this?

Yes. If I may add your S-o-b I could commit it right away.

Thanks, Jan

> diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
> index c8dc8ba..29149d1 100644
> --- a/xen/common/spinlock.c
> +++ b/xen/common/spinlock.c
> @@ -132,7 +132,7 @@ static always_inline u16
> observe_head(spinlock_tickets_t *t)
> 
>  void _spin_lock(spinlock_t *lock)
>  {
> -    spinlock_tickets_t tickets = { .tail = 1, };
> +    spinlock_tickets_t tickets = SPINLOCK_TICKET_INC;
>      LOCK_PROFILE_VAR;
> 
>      check_lock(&lock->debug);
> diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
> index 311685a..9286543 100644
> --- a/xen/include/xen/spinlock.h
> +++ b/xen/include/xen/spinlock.h
> @@ -132,6 +132,8 @@ typedef union {
>      };
>  } spinlock_tickets_t;
> 
> +#define SPINLOCK_TICKET_INC { .head_tail = 0x10000, }
> +
>  typedef struct spinlock {
>      spinlock_tickets_t tickets;
>      u16 recurse_cpu:12;




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