From: Jim Fehlig <jfehlig@suse.com>
To: Olaf Hering <olaf@aepfle.de>
Cc: andrew.cooper3@citrix.com, xen-devel@lists.xen.org,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
Ian Campbell <Ian.Campbell@citrix.com>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: new knob to tweak caching mode for backends
Date: Tue, 27 May 2014 10:50:10 -0600 [thread overview]
Message-ID: <5384C242.6000102@suse.com> (raw)
In-Reply-To: <20140526170617.GA29136@aepfle.de>
Olaf Hering wrote:
> Currently libxl (and xend) has no knob to control cache mode of backend
> driver for block devices. libvirt and qemu have:
> cache=off|none|directsync|writeback|unsafe|writethrough.
>
> The xen qdisk driver in qemu defaults to "writeback". If the diskspec in
> domU…cfg has 'direct-io-safe' then qdisk will default to directsync AIO.
>
> I think these defaults are fine as they provide some sort of data
> integrity.
>
>
> But there is one issue: all the flushing thats going on during guest
> triggered writes does slows down the guest. There should be a knob to
> skip the regular flushes on the host. If the given backing file will
> contain throw-away data its up the the admin to make this decision.
>
ACK to the idea of admin control of cache mode. As you say, admins
already enjoy this capability with libvirt and qemu.
Regards,
Jim
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next prev parent reply other threads:[~2014-05-27 16:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-26 17:06 new knob to tweak caching mode for backends Olaf Hering
2014-05-27 16:50 ` Jim Fehlig [this message]
2014-05-27 17:08 ` Stefano Stabellini
2014-05-27 20:18 ` Jim Fehlig
2014-05-28 8:53 ` Olaf Hering
2014-05-28 11:26 ` Stefano Stabellini
2014-06-10 13:34 ` Ian Jackson
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