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I'm been trying to wrap my head around all this memory barrier business, and I'm slowly grasping the inter-CPU behaviours. Barriers with regard to devices still has me a bit confused though. The deviceiobook document and memory-barriers.txt both make it clear that memory operations to devices are strictly ordered from a single CPU. When more CPUs are involved, things get a bit fuzzier. memory-barriers.txt seems to suggest that mmiowb() is only needed before an unlock under special circumstances, but deviceiobook states that mmiowb() should be used before all unlocks where the writeX():s aren't followed by a readX() (which would flush the writes anyway). Grepping the tree indicates that mmiowb() isn't used that often, but according to deviceiobook, they should be plentiful. This leads me to believe that memory-barriers.txt is closer to the truth, but then the question is what those special cirumstances that require mmiowb() are. Any clarifications you can provide are very welcome. :) Rgds Pierre - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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