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Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers
From: |
Christoph Hellwig |
Subject: |
Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk |
Date: |
Wed, 24 Nov 2010 17:58:35 +0100 |
User-agent: |
Mutt/1.3.28i |
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.
- [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Stefano Stabellini, 2010/11/24
- Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Gerd Hoffmann, 2010/11/24
- Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk,
Christoph Hellwig <=
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Jeremy Fitzhardinge, 2010/11/24
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Christoph Hellwig, 2010/11/24
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Stefano Stabellini, 2010/11/24
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Kevin Wolf, 2010/11/26
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Christoph Hellwig, 2010/11/26
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Stefano Stabellini, 2010/11/26
- Message not available
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Ian Jackson, 2010/11/25
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Jeremy Fitzhardinge, 2010/11/25
- Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk, Christoph Hellwig, 2010/11/25