svn commit: r223464 - head/sys/vm

[Attilio Rao]

2011/6/24 Jayachandran C. <c.jayachandran at gmail.com>:
> On Fri, Jun 24, 2011 at 1:33 AM, Alan Cox <alc at rice.edu> wrote:
>> On 6/23/2011 1:30 PM, Warner Losh wrote:
>>>
>>> On Jun 23, 2011, at 2:17 AM, Bjoern A. Zeeb wrote:
>>>
>>>> On Jun 23, 2011, at 5:24 AM, Alan Cox wrote:
>>>>
>>>>> Author: alc
>>>>> Date: Thu Jun 23 05:23:59 2011
>>>>> New Revision: 223464
>>>>> URL: http://svn.freebsd.org/changeset/base/223464
>>>>>
>>>>> Log:
>>>>> Revert to using the page queues lock in vm_page_clear_dirty_mask() on
>>>>> MIPS.  (At present, although atomic_clear_char() is defined by atomic.h
>>>>> on MIPS, it is not actually implemented by support.S.)
>>>>
>>>> Thanks,
>>>> and good catch on the atomics even if not planned, just in time for 9.0:)
>>>
>>> Yea, there's some work there to fix them...  Not sure we can even fix some
>>> of them atomically...
>>>
>>
>> I'm not sure that I understand what you mean by the second statement.  Can
>> you elaborate?  The 8- and 16-bit operations should be no less "atomic" than
>> the 32- and 64-bit operations.  In general, regardless of the size of the
>> operation, the "sc" instruction may fail and the whole operation has to be
>> restarted if another processor (or I/O device) performs a concurrent, cache
>> coherent store to the same location (or even cache line) as the "ll" and
>> "sc" instructions are operating on.  On the other hand, if the "sc"
>> instruction succeeds, whether you used it to change all of the 32 bits or
>> just 8 of the 32 bits, it should appear as an atomic change to any other
>> processor.
>
> I will try out an implementation and see if this works on XLR, if so
> this is something we can add to support.S

There is a chance we can leave all the atomic support inlined in
atomic.h? When I looked into it, my opinion is that support.S part is
just in the wrong place (and Warner didn't have a good explanation for
it, so I don't see a problem about moving anything to atomic.h).

Attilio


-- 
Peace can only be achieved by understanding - A. Einstein