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Re: [Xen-devel] IO speed limited by size of IO request (for RBD driver)


> When using Ceph, are you using the Linux kernel backend (blkback), Qemu
> or blktap?

I've tried both :
 - Using the RBD kernel driver in dom0 and using phy:/dev/rbd/xxx/xxx
in the vm config
 - Using a custom blktap driver

and I'm observing the same level of performance with both. And it's
while debugging that custom blktap driver, trying to find bottle neck
that I stumbled on the 44k limit.

> I've been working on expanding the number of segments that a request can
> hold, and the patches just went upstream for the next Linux kernel
> (3.10), you might want to test them, they can be found in the following
> git repo:

Oh, indeed, that's really interesting, I'll give it a shot. I'm not
sure how realistic it'll be for me to update all the VM kernel to
something that recent but at least I'll confirm the problem.



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