Messages in this thread | | | From | Keith Owens <> | Subject | Re: Cache coherency... and locking | Date | Fri, 21 Jul 2000 21:24:52 +1000 |
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On Fri, 21 Jul 2000 12:57:21 +0200, Manfred Spraul <manfred@colorfullife.com> wrote: >Keith Owens wrote: >> Linux requires strong write ordering[*]. That is, write A followed by >> write B will appear in memory in the order of A then B. So if any >> write on processor 1 is committed to memory then all preceding writes >> by processor 1 must already have been committed to memory. >> >Are you sure? Do you know a certain function that relies on strong write >ordering?
I could not find an absolute statement of this requirement, just lots of mail about spinlock optimisation that assume strong write ordering. See http://www.uwsg.iu.edu/hypermail/linux/kernel/9911.3/0148.html where Linus says "Basically, everybody agrees on ordering of writes". It would be nice if the kernel gods made a definitive statement about the need or otherwise for strong write ordering.
>Neither ia64 nor the other RISC processors guarantee strong write >ordering.
IA64 load.acquire and store.release are available to do strong write ordering, although the default option is weak order.
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