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[Xen-users] tap:aio Performance


Originally we had tried 3.0.4-0 with loop back mounted file systems.
For some reason the dom0 crashed (after running for a day or so).  It
did this a couple of times on one host server for us, and again once on
another server.

We have just tried 3.0.4-1 with tap:aio file systems on the domUs. After that we've gone a couple of days with no kernel crash. Good so far.

However it seems that performance is a lot slower.

e.g. on a domU:
:/$ time sudo du -s
2020684 .

real    9m25.646s
user    0m0.044s
sys     0m0.144s

On a laptop with a puny 5400 rpm drive: $ time sudo du -s
86923472        .

real    0m18.376s
user    0m0.532s
sys     0m10.737s

And things like bonnie seem to make no real progress.

And on startup things 'seem' slower.

When I run xentop the VBD* columns are all zero (cf. when we were using loop back mounted files and they showed disk IO).

With xen 3.0.4 how does one identify how much IO each domU is doing? Also how does one associate a tapdisk process to a domU? Run xm block-list for each domU (seems awkward).

Are there any options to tune disk IO with blk tap?  On the dom0 or domU?

Has anyone else experienced slower disk IO with 3.0.4/blktap?

Any other information I can provide?

Regards, Peter

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