From: Paolo Bonzini <pbonzini@redhat.com>
To: Alex Bligh <alex@alex.org.uk>
Cc: Ian Campbell <Ian.Campbell@citrix.com>,
Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>,
George Dunlap <george.dunlap@eu.citrix.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
qemu-devel@nongnu.org, xen-devel <xen-devel@lists.xen.org>,
Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: [Qemu-devel] [Xen-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes.
Date: Tue, 19 Mar 2013 12:49:45 +0100 [thread overview]
Message-ID: <514850D9.5010700@redhat.com> (raw)
In-Reply-To: <45EC1ED73B198669B314A507@nimrod.local>
Il 19/03/2013 12:44, Alex Bligh ha scritto:
> If this isn't true, we have a problem anyway with (e.g.) emulated
> devices which don't use O_DIRECT anyway.
Yes, though that would be a libxl bug, not a QEMU bug.
> And I had thought (I may be
> wrong) using O_DIRECT does not guarantee no read caching with NFS;
> O_DIRECT merely guarantees the page cache is not used under Linux
> and isn't defined under POSIX:
> http://www.spinics.net/lists/linux-nfs/msg17472.html
Read caching on the server is fine, because it is the same server that
was used for the writes.
O_DIRECT bypasses the client's page cache, and that's enough for our
purposes.
> If it were just a write caching issue, we could use O_DSYNC instead of
> O_DIRECT, which would at least ensure the copy from userspace.
O_DSYNC is not necessary. We do issue the appropriate fsync/fdatasync.
What O_DSYNC does is add an implicit fdatasync after every write,
basically.
Paolo
next prev parent reply other threads:[~2013-03-19 11:50 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-18 12:18 [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes Alex Bligh
2013-03-18 13:03 ` Stefan Hajnoczi
2013-03-18 13:19 ` Alex Bligh
2013-03-18 13:32 ` Paolo Bonzini
2013-03-18 13:49 ` Alex Bligh
2013-03-18 14:05 ` Paolo Bonzini
2013-03-18 14:30 ` Alex Bligh
2013-03-18 14:49 ` Paolo Bonzini
2013-03-18 15:40 ` Alex Bligh
2013-03-18 16:19 ` Paolo Bonzini
2013-03-18 16:53 ` Alex Bligh
2013-03-18 17:38 ` George Dunlap
2013-03-18 17:47 ` Alex Bligh
2013-03-18 18:00 ` Paolo Bonzini
2013-03-19 10:06 ` [Qemu-devel] [Xen-devel] " George Dunlap
2013-03-19 10:43 ` Paolo Bonzini
2013-03-19 10:51 ` George Dunlap
2013-03-19 11:14 ` Paolo Bonzini
2013-03-19 11:21 ` George Dunlap
2013-03-19 15:12 ` George Dunlap
2013-03-19 15:29 ` George Dunlap
2013-03-19 19:15 ` Alex Bligh
2013-03-20 10:24 ` Stefano Stabellini
2013-03-20 10:37 ` George Dunlap
2013-03-20 11:08 ` Paolo Bonzini
2013-03-20 11:20 ` Alex Bligh
2013-03-20 11:57 ` David Scott
2013-03-19 11:44 ` Alex Bligh
2013-03-19 11:49 ` Paolo Bonzini [this message]
2013-03-19 15:13 ` Stefano Stabellini
2013-03-19 16:53 ` Paolo Bonzini
2013-03-19 17:03 ` Stefano Stabellini
2013-03-20 8:33 ` Alex Bligh
2013-03-20 9:26 ` Paolo Bonzini
2013-03-29 17:19 ` Stefano Stabellini
2013-03-31 19:53 ` Alex Bligh
2013-04-01 15:32 ` [Qemu-devel] [PATCH] [RFC] Xen PV backend: Move call to bdrv_new from blk_init to blk_connect Alex Bligh
2013-04-01 15:44 ` Stefano Stabellini
2013-04-01 20:56 ` Alex Bligh
2013-04-02 11:08 ` Stefano Stabellini
2013-04-05 10:31 ` [Qemu-devel] [PATCHv2 1/2] " Alex Bligh
2013-04-05 10:31 ` [Qemu-devel] [PATCHv2 2/2] Xen PV backend: Disable use of O_DIRECT by default as it results in crashes Alex Bligh
2013-04-05 14:22 ` [Qemu-devel] [PATCHv2 1/2] Xen PV backend: Move call to bdrv_new from blk_init to blk_connect Stefano Stabellini
2013-04-05 15:42 ` [Qemu-devel] [PATCHv3 " Alex Bligh
2013-04-05 15:42 ` [Qemu-devel] [PATCHv3 2/2] Xen PV backend: Disable use of O_DIRECT by default as it results in crashes Alex Bligh
2013-04-05 15:43 ` [Qemu-devel] [PATCHv2 1/2] Xen PV backend: Move call to bdrv_new from blk_init to blk_connect Alex Bligh
2013-04-05 10:32 ` [Qemu-devel] [PATCHv2 1/2] Xen PV backend (for qemu-upstream-4.2-testing): " Alex Bligh
2013-04-05 10:32 ` [Qemu-devel] [PATCHv2 2/2] Xen PV backend (for qemu-upstream-4.2-testing): Disable use of O_DIRECT by default as it results in crashes Alex Bligh
2013-04-05 10:34 ` [Qemu-devel] [PATCH] [RFC] Xen PV backend: Move call to bdrv_new from blk_init to blk_connect Alex Bligh
2013-04-01 16:35 ` [Qemu-devel] [Xen-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes Alex Bligh
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