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Re: [Xen-users] Poor Windows 2003 + GPLPV performance compared to VMWare

On 14/09/12 18:04, Ian Campbell wrote:
> On Thu, 2012-09-13 at 13:25 +0100, Adam Goryachev wrote:
>> Then, the user ran the above process, and got consistently, results of
>> approx 2500 transactions per second
> Are you certain the GPLPV drivers have taken hold and you aren't using
> emulated devices?

Within Windows, Device Manager shows the Disk Drives as "XEV PV DISK
SCSI Disk Device", this is the newest one which it detected and
installed after I changed the config from hda to xvda.

> I don't know how you can tell from within Windows but from dom0 you can
> look in the output of "xenstore-ls -fp" for the "state" node associated
> with each device frontend -- they should be in state 4 (connected).

root@pm08:~# xenstore-ls -fp|grep state|grep vbd
/local/domain/0/backend/vbd/8/51712/state = "4"   (n0,r8)
/local/domain/8/device/vbd/51712/state = "4"   (n8,r0)

I assume dom id 8 is the VM, and dom0 is the first line above.

> [...]
>> memory        = 4096
>> shadow_memory    = 12
> This seems low to me. The default is 1M per CPU, plus 8K per M of RAM,
> which is 4M + 8*4096K = 4M+32M = 36M. Do you have any reason to second
> guess this? (Usually this option is used to increase shadow RAM where
> the workload demands it).

OK, I must admit I have no idea, I copied this value from an example a
long time ago, and I've just copied it into each new vm as I go.

From here:
It says:
The shadow_memory directive specifies the amount of memory to use for
shadow page tables. (Shadow page tables, of course, are the
aforementioned copies of the tables that map process-virtual memory to
physical memory.) Xen advises allocating at least 2KB per MB of domain
memory, and âa fewâ MB per virtual CPU. Note that this memory is in
addition to the domUâs allocation specified in the memory line.

I'm not really sure where to find definitive documentation on all the
config file options within xen.... I will re-run the test with
shadow_memory = 36 and let you know. Was going to run it now and advise,
but some scheduled task has started, so will wait until it is finished
and re-test.

> Does your system have HAP (hardware assisted paging, EPT or NPT on
> Intel/AMD respectively)?

(XEN) HVM: ASIDs enabled.
(XEN) SVM: Supported advanced features:
(XEN)  - Nested Page Tables (NPT)
(XEN)  - Last Branch Record (LBR) Virtualisation
(XEN)  - Next-RIP Saved on #VMEXIT
(XEN)  - Pause-Intercept Filter
(XEN) HVM: SVM enabled
(XEN) HVM: Hardware Assisted Paging (HAP) detected
(XEN) HVM: HAP page sizes: 4kB, 2MB, 1GB

I'm guessing that is a yes to HAP and NPT but no for EPT....

This is a AMD Phenom(tm) II X6 1100T Processor

>> device_model    = '/usr/lib/xen-default/bin/qemu-dm'
>> localtime    = 1
>> name        = "vm1"
>> cpus        = "2,3,4,5"    # Which physical CPU's to allow
> Have you pinned dom0 to use pCPU 1 and/p pCPUs > 6?

No, how should I pin dom0 to cpu0 ?

Also, xm vcpu-list shows this:
xm vcpu-list
Name                                ID  VCPU   CPU State   Time(s) CPU
Domain-0                             0     0     0   r--   34093.4 any cpu
Domain-0                             0     1     5   -b-    1239.3 any cpu
Domain-0                             0     2     1   -b-    1134.4 any cpu
Domain-0                             0     3     3   -b-    1049.9 any cpu
Domain-0                             0     4     0   -b-    1340.5 any cpu
Domain-0                             0     5     2   -b-    1123.2 any cpu
vm1                                  9     0     2   -b-      20.5 2-5
vm1                                  9     1     4   -b-      15.2 2-5
vm1                                  9     2     3   -b-      14.9 2-5
vm1                                  9     3     4   -b-      15.1 2-5

I've set the vm to use cpus 2,3,4,5 but how do I force it so:
vcpu 0 = 2
vcpu 1 = 3
vcpu 2 = 4
vcpu 3 = 5

Without running:
xm vcpu-pin vm1 0 2
xm vcpu-pin vm1 1 3
xm vcpu-pin vm1 2 4
xm vcpu-pin vm1 3 5

> How many dom0 vcpus have you configured?

I assume by default it takes all of them...

> Does your system have any NUMA properties?

I don't really understand this question.... is there a simple method to
check? It is a AMD Phenom(tm) II X6 1100T Processor on a reasonable
desktop motherboard, nothing fancy....

> And as James suggests it would also be useful to benchmark iSCSI running
> in dom0 and perhaps even running on the same system without Xen (just
> Linux) using the same kernel. I'm not sure if VMware offers something
> similar which could be used for comparison.

Well, that is where things start to get complicated rather quickly...
There are a lot of layers here, but I'd prefer to look at the issues
closer to xen first, since vmware was working from an identically
configured san/etc, so nothing at all has changed there. Ultimately, the
san is using 3 x SSD in RAID5. I have done various testing in the past
from plain linux (with older kernel 2.6.32 from debian stable) and
achieved reasonable figures (I don't recall exactly).

Thank you for your responses, if there is any further information I can
provide, or additional suggestions you are able to make, I'd be really


Adam Goryachev
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