RE: [Xen-devel] Poor performance on HVM (kernbench)

[Daniel Magenheimer <dan.magenheimer@xxxxxxxxxx>]

This doesn't answer the HVM question but it appears that
you are running guests with 1 vCPU but comparing against
a dual-CPU native.  True?

> -----Original Message-----
> From: Todd Deshane [mailto:deshantm@xxxxxxxxx]
> Sent: Wednesday, September 10, 2008 12:23 PM
> To: xen-devel mailing list
> Subject: [Xen-devel] Poor performance on HVM (kernbench)
> 
> 
> Hi All,
> 
> We are continuing our Xen vs. KVM benchmarking that I 
> presented at Xen summit.
> 
> This time, we are focusing on newer versions and also planning to
> include Xen HVM
> and KVM with PV drivers results. As well as adding some more tests.
> 
> I have setup Xen 3.3 from source, and am using Linux 2.6.27-rc4 for
> all the guests.
> 
> Below are some raw kernbench results, which clearly show that 
> I have a problem
> with Xen HVM. It may just be a configuration issue, but we have tried
> all that we
> could think of so far (i.e file:, instead of tap:aio). I have also
> tried xen-unstable and
> it doesn't seem to produce any better results. I am also in the
> process of trying
> kernbench on older versions of Xen HVM.
> 
> here is the xm command line
> xm create /dev/null name=benchvm0 memory=2048
> kernel="/usr/lib/xen/boot/hvmloader" builder="hvm"
> device_model=/usr/lib64/xen/bin/qemu-dm
> disk=file:/root/benchvm/bin/img-perf_xen_hvm_test1/image-0.img,hda,w
> vnc=1 vncdisplay=0 vif=mac=AA:BB:CC:DD:EE:00,bridge=br0
> vif=mac=AA:BB:CC:DD:EE:7b,bridge=br1 vncviewer="yes"
> on_poweroff=destroy on_reboot=restart on_crash=preserve
> 
> I will also consider an IO test, such as iozone to see if
> the disk IO problems are a cause. The dom0 cpu
> doesn't seem to be under much load at all during the
> kernbench run.
> 
> System time on the kernbench run is 1/2 of the time, so does
> that suggest either disk IO or guest scheduling problem?
> 
> System time on the other cases is 1/4 or less on the other
> cases.
> 
> If anybody has any ideas, suggestions, or can even run Xen 
> HVM kernbench
> vs. native on their setup to compare against that would be 
> very helpful.
> 
> The system setup is a Intel core2 dual 4 GB of ram.
> The HVM guest does run the libata driver similar to KVM with 
> emulated drivers.
> 
> Thanks,
> Todd
> 
> KVM PV drivers
> 
> Average Optimal load -j 4 Run (std deviation):
> Elapsed Time 527.572 (0.681337)
> User Time 404.3 (0.982141)
> System Time 122.552 (0.468636)
> Percent CPU 99 (0)
> Context Switches 116020 (180.82)
> Sleeps 31307 (94.2072)
> 
> 
> KVM Emulated drivers
> 
> Average Optimal load -j 4 Run (std deviation):
> Elapsed Time 527.968 (0.450744)
> User Time 403.95 (0.342929)
> System Time 122.134 (0.550709)
> Percent CPU 99 (0)
> Context Switches 115907 (214.3)
> Sleeps 31302.4 (88.7175)
> 
> Xen PV
> 
> Average Optimal load -j 4 Run (std deviation):
> Elapsed Time 446.876 (0.130115)
> User Time 392.088 (0.339367)
> System Time 54.76 (0.391088)
> Percent CPU 99 (0)
> Context Switches 64601.4 (163.314)
> Sleeps 31214.8 (183.53)
> 
> 
> 
> Xen HVM
> 
> Average Optimal load -j 4 Run (std deviation):
> Elapsed Time 2081.71 (34.0459)
> User Time 617.36 (3.61771)
> System Time 1430.36 (28.3309)
> Percent CPU 98 (0)
> Context Switches 331843 (5283.28)
> Sleeps 37329.8 (91.538)
> 
> 
> KVM Native (Linux)
> 
> Average Optimal load -j 8 Run (std deviation):
> Elapsed Time 216.076 (0.121778)
> User Time 381.122 (0.259557)
> System Time 43.242 (0.278783)
> Percent CPU 196 (0)
> Context Switches 75483.2 (389.988)
> Sleeps 38078.8 (354.267)
> 
> 
> Xen native 2.6.18.8 dom0 kernel
> 
> Average Optimal load -j 8 Run (std deviation):
> Elapsed Time 228.504 (0.0808084)
> User Time 384.014 (0.657632)
> System Time 64.028 (0.733669)
> Percent CPU 195.8 (0.447214)
> Context Switches 35270.4 (264.36)
> Sleeps 39493.4 (266.222)
> 
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>

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