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

[Radhya sahal <rad_cs_2006@xxxxxxxxx>]

 

HI Pasi,
thanks for your cooperation,this the XML configuration VM file
name = "vm2"
uuid = "70bf5c52-91ed-fbd5-4eb7-f6acc52c3168"
maxmem = 2277
memory = 1024
vcpus = 1
bootloader = "/usr/bin/pygrub"
kernel = "/var/lib/xen/boot_kernel.313tN4"
ramdisk = "/var/lib/xen/boot_ramdisk.vV9Kd9"
extra = "ro root=/dev/VolGroup00/LogVol00 rhgb quiet"



vfb = [ "type=vnc,vncunused=1,keymap=en-us" ]
disk = [ "tap:aio:/var/lib/xen/images/vm2.img,xvda,w" ]
vif = [ "mac=00:16:36:1e:3a:dc,bridge=virbr0,script=vif-bridge,vifname=vif2.0" ]
 i am new user for xen so i think maybe you the backend in xen tap:aio ??
how can be sure the  VM cache is empty with out restart VM??
 

--- On Sun, 7/24/11, Pasi Kärkkäinen <pasik@xxxxxx> wrote:

From: Pasi Kärkkäinen <pasik@xxxxxx>
Subject: Re: [Xen-users] how can empty xen disk cache??
To: "Radhya sahal" <rad_cs_2006@xxxxxxxxx>
Cc: "xen list" <xen-users@xxxxxxxxxxxxxxxxxxx>
Date: Sunday, July 24, 2011, 3:21 AM

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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