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
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5384C242.6000102@suse.com \
--to=jfehlig@suse.com \
--cc=Ian.Campbell@citrix.com \
--cc=Ian.Jackson@eu.citrix.com \
--cc=andrew.cooper3@citrix.com \
--cc=olaf@aepfle.de \
--cc=stefano.stabellini@eu.citrix.com \
--cc=xen-devel@lists.xen.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.