Re: [Xen-devel] [PATCH v5 1/4] VT-d PI: track the number of vcpus on pi blocking list

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.09.17 at 11:55, <JBeulich@xxxxxxxx> wrote:
>>>> On 01.09.17 at 10:37, <chao.gao@xxxxxxxxx> wrote:
>> it seems add_sized() won't be a LOCKed instruction.
>> #define build_add_sized(name, size, type, reg) \
>>     static inline void name(volatile type *addr, type val)              \
>>     {                                                                   \
>>         asm volatile("add" size " %1,%0"                                \
>>                      : "=m" (*addr)                                     \
>>                      : reg (val));                                      \
>>     }
> 
> Oh, you're right. But then I'd still like you to not add a new
> user, as I don't see why it was introduced in the first place:
> Independent of architecture it is equivalent to
> 
> write_atomic(p, read_atomic(p) + c)
> 
> and hence I'd like to get rid of it as misleading/redundant.

Actually, on x86 it still is a bit better than the generic replacement,
i.e. it would only be worthwhile dropping the custom ARM variant
in favor of a generic one. Keep using it here then.

Jan


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