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

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Mon, Jul 25, 2011 at 12:24:55PM -0700, Radhya sahal wrote:
>    --- On Mon, 7/25/11, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> 
>      T hank's Pasi ,
>      I tried to run this command drop cache in VM and physical(dom0) before i
>      put my question in the group !!!
>      echo 3 >/proc/sys/vm/drop_caches
>      dom0 actually empty cache but there is not any effect the files in VM
>      still in the cache??
> 

So then Xen dom0 is NOT caching anything.
Your problem is somewhere else!

Perhaps hardware RAID controller (with memory cache onboard) ?

-- Pasi

>      On Sun, Jul 24, 2011 at 08:45:49AM -0700, Radhya sahal wrote:
>      >    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"
>      >    on_poweroff = "destroy"
>      >    on_reboot = "restart"
>      >    on_crash = "restart"
>      >    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??
>      >
> 
>      So yeah, you're using tap:aio: backend.
>      You shouldn't have any dom0 caching then.
> 
>      Do you perhaps have a RAID controller with memory cache module?
> 
>      You could try running the "drop caches" in dom0, and see if that changes
>      anything..
> 
>      -- Pasi
> 
>      >
>      >    --- On Sun, 7/24/11, Pasi Kärkkäinen <[1]pasik@xxxxxx> wrote:
>      >
>      >      From: Pasi Kärkkäinen <[2]pasik@xxxxxx>
>      >      Subject: Re: [Xen-users] how can empty xen disk cache??
>      >      To: "Radhya sahal" <[3]rad_cs_2006@xxxxxxxxx>
>      >      Cc: "xen list" <[4]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 <[1][5]pasik@xxxxxx>
>      wrote:
>      >      >
>      >      >      From: Pasi Kärkkäinen <[2][6]pasik@xxxxxx>
>      >      >      Subject: Re: [Xen-users] how can empty xen disk cache??
>      >      >      To: "Mark Pryor" <[3][7]tlviewer@xxxxxxxxx>
>      >      >      Cc: "Radhya sahal" <[4][8]rad_cs_2006@xxxxxxxxx>,
>      >      >      "[5][9]xen-users@xxxxxxxxxxxxxxxxxxx"
>      >      <[6][10]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 <[7][11]rad_cs_2006@xxxxxxxxx>
>      >      >      >    To: [8][12]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
>      >
>      > References
>      >
>      >    Visible links
>      >    1. file:///mc/compose?to=[13]pasik@xxxxxx
>      >    2. file:///mc/compose?to=[14]pasik@xxxxxx
>      >    3. file:///mc/compose?to=[15]tlviewer@xxxxxxxxx
>      >    4. file:///mc/compose?to=[16]rad_cs_2006@xxxxxxxxx
>      >    5. file:///mc/compose?to=[17]xen-users@xxxxxxxxxxxxxxxxxxx
>      >    6. file:///mc/compose?to=[18]xen-users@xxxxxxxxxxxxxxxxxxx
>      >    7. file:///mc/compose?to=[19]rad_cs_2006@xxxxxxxxx
>      >    8. file:///mc/compose?to=[20]xen-users@xxxxxxxxxxxxxxxxxxx
> 
> References
> 
>    Visible links
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>    2. file:///mc/compose?to=pasik@xxxxxx
>    3. file:///mc/compose?to=rad_cs_2006@xxxxxxxxx
>    4. file:///mc/compose?to=xen-users@xxxxxxxxxxxxxxxxxxx
>    5. file:///mc/compose?to=pasik@xxxxxx
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>   11. file:///mc/compose?to=rad_cs_2006@xxxxxxxxx
>   12. file:///mc/compose?to=xen-users@xxxxxxxxxxxxxxxxxxx
>   13. file:///mc/compose?to=pasik@xxxxxx
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