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[Xen-devel] Does Xen force all AIO be synchronous?



Hi,

I have these questions for a while. As AIO can help improve better performance and Linux kernel keeps tunning the AIO path, more and more IOs can be expected to take AIO path instead of regular I/O path.

First Question:
If we consider Xen, do we need to do AIO both in the domain0 and guest domains at the same? For example, considering two situations, let a full virtualized guest domain still do regular I/O and domain0 (vbd back end driver) do AIO; or let both full-virtualized guest domain and domain0 do AIO. What is possible performance difference here?

Second Question:
Does Domain0 always wait till AIO data is available and then notify guest domain? or Domain0 will issue an interrupt immediately to notify guest domain0 when AIO is queued? If the first case is true, then all AIOs will become synchronous.

Third Question:
Does Xen hypervisor change the behavior of Linux I/O scheduler more or less?

Four Question:
Will AIO have different performance impact on para-virtualized domain and full-virtualized domain respectively?

Thanks,

Liang


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