[uml-devel] parallel I/O

[Nicolas Boullis <nicolas.boullis@ecp.fr>]

Hi,

I've been using uml on production servers for months, and have been
quite happy with it, except for I/O performance.

I was using the user-mode-linux package from Debian Etch, based on
2.6.18, and compiled with CONFIG_BLK_DEV_UBD_SYNC. Disabling this option
of course helps performance, but I feel that it's somewhat unsafe if the
host crashes... Moreover, I don't think it helps read performance.

As far as I can see, if one wants both safety and performance, the I/O
must not be serialized. So I decided to give it a try.

The first step was to run a per-device I/O thread. This improves
slightly the performance with several UBD devices: I/O on one device do
not block I/O on another device. Moreover, that helps to implement
parallelized I/O.

Then I managed to run several parallel threads per device. As far as I
am concernced, that much improves the performance. But currently, my
code is more a dirty proof-of-concept than a clean patch.

Would you be interested by my work?


Cheers,

Nicolas Boullis
École Centrale Paris

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