Re: [PATCH 3/3] kvm-s390: streamline memslot handling - rebased

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Avi Kivity wrote:
> Christian Ehrhardt wrote:  
>>>
>>> Really need that smp_mb__after_clear_bit ? AFAIK test_and_clear_bit
>>> implies a barrier?
>>>   
>>
>> Well I agree that practically test_and_clear_bit has a barrier on 
>> s390, but as far as I read Documentation/atomic_ops.txt at line 
>> 339-360 I think the interface does not imply it so I wanted to add it 
>> explicitly. I would be happy if someone really knows the in depth 
>> details here and corrects me :-)
>
> IIUC rmw bitops are full memory barriers.  The non-rmw (from the 
> caller's perspective), clear_bit() and set_bit(), are not.
>
>
Ok, as the real implementation has one + memory-barriers.txt describing 
it with barrier and finally include/asm-generic/bitops/atomic.h 
descirbes it that way too I think I can drop the explicit smb_wb from my 
patch in the next update (I wait a bit to give the discussion about the 
wati/bits a bit more time).

Hmm ... would that be worth a clarifying patch to atomic_ops.txt that 
confused me in the first place ?

-- 

Grüsse / regards, Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization