[uml-devel] What's the status of UBD with AIO?

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

Hello,

I've been using UML for production servers for years, but I'm now
experiencing some performance problems with UBD (I've always used it
with CONFIG_BLK_DEV_UBD_SYNC).

I tried to patch UBD to run several I/O threads that perform the
requests in parallel. It improved performances significantly, but not
enough for me.

Using UML without CONFIG_BLK_DEV_UBD_SYNC improves performance a lot,
but the the guest has no way to ensure that it's data is actually
written on the disc. I certainly don't wan this for, e.g., a mail
server, or my users will kill me.

I read that there used to be some work done about using AIO for UBD,
with the device file opened with O_DIRECT. As far as I can see, it lokks
exactly like what I need. I read that Jeff reverted the change just
before 2.6.14, but he was then saying that he would re-add it soon...

What's the status of UBD with AIO nowadays? Does anyone use it? Where
can I find a patch that implements this?


Regards,

Nicolas

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