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I'm a little confused about the image. How is it possible to write A simultaneously with read B? If we use a write buffer for write A, wouldn't we only be able to commit the write A after read B is done, so the line for write A should be longer than on the left?


@huehue I don't think so - the reason the write to A is permitted to temporally overlap with the read of B is that these operations are independent from the perspective of the processor, so there is also no prohibition on committing the write to A based on whether the pending read of B has completed. I think the lines associated with these operations show the time over which an operation is "in flight" - so the end of the line for the write to A is when the write actually appears to other processors, and it doesn't mean that the processor is actually performing work associated with writing A and reading B simultaneously.