svn commit: r235931 - head/sys/powerpc/include
Marcel Moolenaar
marcel at xcllnt.net
Thu May 24 22:07:20 UTC 2012
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
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