On Mar 7, 2012 4:33 AM, "Jan Beulich" [off-list ref] wrote:

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On 06.03.12 at 18:20, Konrad Rzeszutek Wilk [off-list ref] wrote:

 -> the usage of XenbusStateInitWait? Why do we introduce that? Looks
like a fix to something.

No, this is required to get the negotiation working (the frontend must
not try to read the new nodes until it can be certain that the backend
populated them). However, as already pointed out in an earlier reply
to Santosh, the way this is done here doesn't appear to allow for the
backend to already be in InitWait state when the frontend gets
invoked.

OK.

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-> XENBUS_MAX_RING_PAGES - why 2? Why not 4? What is the optimal
default size for SSD usage? 16?

What do SSDs have to do with a XenBus definition? Imo it's wrong (and
unnecessary) to introduce a limit at the XenBus level at all - each driver
can do this for itself.

The patch should mention what the benefit of multi ring is.

As to the limit for SSDs in the block interface - I don't think the number
of possibly simultaneous requests has anything to do with this. Instead,
I'd expect the request number/size/segments extension that NetBSD
apparently implements to possibly have an effect.

.. which sounds to me like increasing the bandwidth of the protocol. Should
be mentioned somewhere in the git description.

Jan