Messages in this thread | | | Date | Tue, 19 Feb 2002 12:23:10 -0800 | From | Jesse Barnes <> | Subject | Re: readl/writel and memory barriers |
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On Tue, Feb 19, 2002 at 03:11:45PM -0500, Dan Maas wrote: > I have a hunch that many drivers will break if you change the semantics of > readX/writeX from in-order to out-of-order - lots of drivers are only > developed & tested on x86, which completely hides the issue...
Fortunately, I don't think things are quite that bad. As David pointed out, on ia64 the readX/writeX stuff is ordered coming out of the CPU, so if you're in a spinlock protected region, for example, all the reads/writes you do will occur in order. The problem that I'm trying to solve is that on some platforms, I/O space references won't necessarily occur in order if they come from different CPUs. E.g. after you do some I/O and drop a spinlock, another CPU may pick it up and start doing some I/O that *may* get intermixed with the I/O from the previous holder of the spinlock unless you explicity barrier said I/O.
Any ideas on how to address this issue? I was thinking of either introducing an I/O space barrier (currently called mmiob() in the 2.5 ia64 patch) or taking the performance hit in mb, rmb, and wmb, as well as readX/writeX to ensure proper ordering. Or, as I mentioned in another mail, we could have a special io_spin_unlock routine that does the barrier for you. Comments?
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