Re: [Xen-devel] why do I get bad disk write performance in the kernel 3.1?

[Roberto Scudeller <beto.rvs@xxxxxxxxx>]

Ian,

That depends on whether Roberto is using xm/xend or xl, I think.
Roberto?

I'm using "xl create windows.cfg"
 

I'm not sure what xend does for 'tap2:aio' if blktap isn't available. I
suspect it doesn't fallback to qdisk. Roberto can you report the content
of xenstore under /local/domain/0/backend/ (use xenstore-ls <path>).

# xenstore-ls /local/domain/0/backend
qdisk = ""
 10 = ""
  51712 = ""
   frontend = "/local/domain/10/device/vbd/51712"
   params = "aio:/local-disk/benchCM-windows-2003-64b-std/xvda"
   frontend-id = "10"
   >   removable = "0"
   bootable = "1"
   state = "4"
   dev = "xvda"
   type = "tap"
   mode = "w"
   feature-barrier = "1"
   info = "0"
   sector-size = "512"
   sectors = "67108864"
   hotplug-status = "connected"
  51728 = ""
   frontend = "/local/domain/10/device/vbd/51728"
   params = "aio:/local-disk/benchCM-windows-2003-64b-std/xvdb"
   frontend-id = "10"
   >   removable = "0"
   bootable = "1"
   state = "4"
   dev = "xvdb"
   type = "tap"
   mode = "w"
   feature-barrier = "1"
   info = "0"
   sector-size = "512"
   sectors = "614400"
   hotplug-status = "connected"
console = ""
 10 = ""
  0 = ""
   frontend = "/local/domain/10/console"
   frontend-id = "10"
   >   state = "1"
   domain = "benchCM-windows-2003-64b-std-test"
   protocol = "vt100"


 

> You could also try the 'file:/local-disk' which will setup a loopback device
> and use that. Try that as well.

This is true with xm/xend but with xl you will need to manually setup
the looback and use phy:/dev/loop in order to perform this experiment.
For xl file: turns into qdisk unless blktap is available.

I'm execute with file:/, but in xenstore-list, continue with qdisk. Look:
device = ""
 suspend = ""
  event-channel = "6"
 vbd = ""
  51712 = ""
   backend = "/local/domain/0/backend/qdisk/10/51712"
   backend-id = "0"
   state = "4"
   virtual-device = "51712"
   device-type = "disk"
   ring-ref = "16383"
   event-channel = "7"
  51728 = ""
   backend = "/local/domain/0/backend/qdisk/10/51728"
   backend-id = "0"
   state = "4"
   virtual-device = "51728"
   device-type = "disk"
   ring-ref = "16371"
   event-channel = "8"

Konrad,
I try with "file://" and result was qdisk again. Do you think is LVM test need?

I testing my windows.cfg in xen 4.1.2-rc1-pre with kernel 2.6.32.43, the result of xenstore-ls:
# xenstore-ls /local/domain/0/backend
vbd = ""
 2 = ""
  51712 = ""
   frontend = "/local/domain/2/device/vbd/51712"
   tapdisk-params = "aio:/disk-local/benchCM-windows-2003-64b-std/xvda"
   params = "/dev/xen/blktap-2/tapdev2"
   physical-device = "fd:2"
   frontend-id = "2"
   >    removable = "0"
   bootable = "1"
   state = "4"
   dev = "xvda"
   type = "phy"
   mode = "w"
   feature-barrier = "1"
   sectors = "67108864"
   info = "0"
   sector-size = "512"
  51728 = ""
   frontend = "/local/domain/2/device/vbd/51728"
   tapdisk-params = "aio:/local-disk/benchCM-windows-2003-64b-std/xvdb"
   params = "/dev/xen/blktap-2/tapdev3"
   physical-device = "fd:3"
   frontend-id = "2"
   >   removable = "0"
   bootable = "1"
   state = "4"
   dev = "xvdb"
   type = "phy"
   mode = "w"
   feature-barrier = "1"
   sectors = "614400"
   info = "0"
   sector-size = "512"
console = ""
 2 = ""
  0 = ""
   frontend = "/local/domain/2/console"
   frontend-id = "2"
   >   state = "1"
   domain = "benchCM-windows-2003-64b-std-test"
   protocol = "vt100"

Why did kernel 3.1 use the qdisk? I want to use blktap backend ('tap2:aio:/disk-local/xvda,xvda,w').

Thanks for help.

-- 
Roberto Scudeller


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