What's the status of UBD with AIO?

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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