[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH] Blktap: Userspace file-based image support. (RFC)

Rusty Russell wrote:
On Mon, 2006-06-19 at 09:19 -0700, Andrew Warfield wrote:
Attached to this email is a patch containing the (new and improved)
blktap Linux driver and associated userspace tools for Xen.  In
addition to being more flavourful, containing half the fat, and
removing stains twice as well as the old driver, this stuff adds a
userspace block backend and let you use raw (without loopback), qcow,
and vmdk-based image files for your domUs.  There's also a fun little
driver that provides a shared-memory block device which, in
combination with OCFS2, represents a cheap-and-cheerful fast shared
filesystem between multiple domUs.

Hi Andrew,

        I like the idea of block servers in userspace, but I'm curious.  When I
wrote the simple share block server I couldn't see an obvious
justification for multiple outstanding requests (with AIO/threads and
all that entails),

Are you thinking of posix-aio? posix-aio is "emulated" with threads and normal read/select calls. The performance isn't that great.

I believe blktap is using linux-aio which doesn't use threads (it uses the linux specific interface). I've seen a number of benchmarks where linux-aio is significantly better than posix-aio.


Anthony Liguori

 so I went for the trivial single request approach.
It seems to me that the backend doesn't have much information the front
end doesn't have.

Just wondered if you'd tried a naive approach first...


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.