svn commit: r235931 - head/sys/powerpc/include

[Marcel Moolenaar]

On May 24, 2012, at 2:13 PM, Nathan Whitehorn wrote:

> On 05/24/12 15:45, Marcel Moolenaar wrote:
>> Author: marcel
>> Date: Thu May 24 20:45:44 2012
>> New Revision: 235931
>> URL: http://svn.freebsd.org/changeset/base/235931
>> 
>> Log:
>>   Fix the memory barriers for CPUs that do not like lwsync and wedge or cause
>>   exceptions early enough during boot that the kernel will do ithe same.
>>   Use lwsync only when compiling for LP64 and revert to the more proven isync
>>   when compiling for ILP32. Note that in the end (i.e. between revision 222198
>>   and this change) ILP32 changed from using sync to using isync. As per Nathan
>>   the isync is needed to make sure I/O accesses are properly serialized with
>>   locks and isync tends to be more effecient than sync.
>> 
> 
> This badly breaks the synchronization primitives. The functions mb()/wmb()/rmb() need to be sync or lwsync on ILP32, not isync.

I guess I misinterpreted your email in which you stated that isync is better.

> Summary:
> 1. *mb() must be lwsync or sync on all machines, except for wmb() which could be eieio
> 2. __ATOMIC_ACQ() must be isync (though could be reduced to lwsync with bus_space changes)
> 3. __ATOMIC_REL() must be lwsync or sync

This is absolutely not what I concluded from our discussions. I have no idea
how we could end up so out of sync...

-- 
Marcel Moolenaar
marcel at xcllnt.net