Date: Thu, 24 May 2012 15:07:03 -0700 From: Marcel Moolenaar <marcel@xcllnt.net> To: Nathan Whitehorn <nwhitehorn@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, Marcel Moolenaar <marcel@freebsd.org>, src-committers@freebsd.org Subject: Re: svn commit: r235931 - head/sys/powerpc/include Message-ID: <EEFFC9C4-7469-4D70-A5C6-7F5CB19CAC28@xcllnt.net> In-Reply-To: <4FBEA493.4020702@freebsd.org> References: <201205242045.q4OKjipb059398@svn.freebsd.org> <4FBEA493.4020702@freebsd.org>
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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@xcllnt.net
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