On Sat, Jul 23, 2011 at 06:46:58PM -0700, Radhya sahal wrote:
> thank's Mark and Pasi,
> i use centos and xen ,either dom0 and vm run centos 5.5.
> in the vm i run java application which it reads e.g( text file ,table in
> database,....).
> in the first read get actual total run-time but if i try to read more than
> one . the file be in cache and get a very very short time ..!!!
> although i try to empty the vm cache and physical(dom0) cache!!!
> echo 3 >/proc/sys/vm/drop_caches
> i want to read more than one to calculate the the right average run-time
> for
> the vm resource allocation and compare this averages with other vm
> resource
> allocations ???
>
I repeat the question: Which disk backend are you using in dom0 for the VM ?
-- Pasi
> --- On Sat, 7/23/11, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
>
> From: Pasi Kärkkäinen <pasik@xxxxxx>
> Subject: Re: [Xen-users] how can empty xen disk cache??
> To: "Mark Pryor" <tlviewer@xxxxxxxxx>
> Cc: "Radhya sahal" <rad_cs_2006@xxxxxxxxx>,
> "xen-users@xxxxxxxxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxxxxxxxx>
> Date: Saturday, July 23, 2011, 6:44 AM
>
> On Fri, Jul 22, 2011 at 07:11:57PM -0700, Mark Pryor wrote:
> >
>
> --------------------------------------------------------------------------
> >
> > From: Radhya sahal <rad_cs_2006@xxxxxxxxx>
> > To: xen-users@xxxxxxxxxxxxxxxxxxx
> > Sent: Friday, July 22, 2011 5:36 PM
> > Subject: [Xen-users] how can empty xen disk cache??
> >
> > hi
> > I am new user for xen
> > i have VM and i run java application on it ..
> > i want to empty cache for vm
> > i do that with
> > echo 3 >/proc/sys/vm/drop_caches
> > and the same command in physical machine
> > but there is not any effect
> > i think the vm have own cache in xen
> > how can empty xen disk cache??
> > thanks
> >
> > check options in /etc/sysconfig/xendomains or (etc/default -- in
> debian)
> > and turn off save/restore.
> >
>
> I don't think the question has nothing to do with save/restore.
>
> Dom0 does not usually cache domU disk IO, unless you're using file:
> backend.
> Which disk backends are you using?
>
> tap:aio and phy: backends bypass the dom0 page cache,
> and thus those backends don't have any caching in xen dom0.
>
> Xen hypervisor itself does not have cache of any kind.
>
> -- Pasi
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