Re: [Xen-users] how can empty xen disk cache??

[Pasi Kärkkäinen <pasik@xxxxxx>]

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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