[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk
I had the discussion with Jeremy in Boston before, but let's repeat it here: - is there actually any pre-existing xen backend that does properly implement empty barries. Back then we couldn't find any. - if this is a new concept to Xen please do not define an empty barrier primitive, but a new flush cache primitive. That one maps natively to the qemu I/O layer, and with recent Linux, NetBSD, Windows, or Solaris guest will be a lot faster than a barrier which drains the queue. Note that what your patch implements actually is a rather inefficient implementation of the latter. You do none of the queue draining which the in-kernel blkback implementation does by submitting the old-style barrier bio. While most filesystem do not care you introduce a quite subtile chance of data corruption for reiserfs, or ext4 with asynchronous journal commits on pre-2.6.37 kernels. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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