Re: [Xen-users] Xen hard-disk performance regression?

[Fabiano Francesconi <fabiano.francesconi@xxxxxxxxx>]

Ok the problem seems solved.
An ##xen irc user, jamon, told me to add 'elevator=noop' as kernel
bootflag in order to disable I/O scheduler on the domU.

This is quite interesting since, as he states "getting different guests
all trying to read/write at the same time with different schedulers, or
even different kernels (linux cf. windows cf. bsd etc.) isn't as good as
letting the host do all the heavy lifting and not have to worry about
different write caches, flushing etc. that different guests might be doing.

Actually I was wondering about my situation. My whole disk is passed
entirely to the domU so this shouldn't be a problem at all.

After rebooting the machine what I get is:

real    0m16.993s
user    0m0.009s
sys     0m1.143s

4 seconds faster than the .29 kernel! Hurray!

At this point I'm still curious about the reasons why this behaviour
changed so unexpectantly and why this 'noop' chages the things so badly
even if my disk belongs entirely to a single domU.

-- 
Fabiano Francesconi [GPG key: 0x81E53461]

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