Date: Thu, 24 May 2012 17:15:15 -0500 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: Marcel Moolenaar <marcel@xcllnt.net> 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: <4FBEB2F3.4060405@freebsd.org> In-Reply-To: <EEFFC9C4-7469-4D70-A5C6-7F5CB19CAC28@xcllnt.net> References: <201205242045.q4OKjipb059398@svn.freebsd.org> <4FBEA493.4020702@freebsd.org> <EEFFC9C4-7469-4D70-A5C6-7F5CB19CAC28@xcllnt.net>
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On 05/24/12 17:07, Marcel Moolenaar wrote: > > 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. It's just in this one single case. Otherwise, it's still faster but doesn't work :) >> 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... > Thanks for the quick change. No idea how we got out of sync. I find all of this synchronization stuff a little mind-bending, so sorry for any miscommunication. __ATOMIC_ACQ() needed to also be isync on ppc64, so I've fixed that up. Things should be good now. -Nathan
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