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xen-devel
RE: [Xen-devel] Benchmarking Xen (results and questions)
David,
Which xen version is this? I'm guessing unstable.
Is this with sedf or bvt? I'm guessing sedf since you're playing around
with periods.
It would be interesting to retry a couple of datapoints with sched=bvt
on the xen command line.
Also, I'd definitely recommend enabling HyperThreading and dedicating
one of the logical CPUs to dom0.
Also, are you sure the drop-off in performance isn't just caused because
of the reduced memory size when you have more VMs? It's probably better
to do such experiments with the same memory size throughout.
Best,
Ian
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> David_Wolinsky@xxxxxxxx
> Sent: 04 August 2005 00:21
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] Benchmarking Xen (results and questions)
>
> Hi all,
>
> Here are some benchmarks that I've done using Xen.
>
> However, before I get started, let me explain some of
> configuration details...
>
> Xen Version SPECjbb
> WebBench
> Linux Distribution Debian 3.1
> HT disabled
> Linux Kernel 2.6.12.2
> Host Patch CK3s
>
>
> Here are the initial benchmarks
>
> SPECJBB WebBench
> 1 Thread 1 Client 2 Clients 4
> Clients 8 Clients
> BOPS TPS TPS TPS TPS
> Host 32403.5 213.45 416.86 814.62 1523.78
> 1 VM 32057 205.4 380.91 569.24 733.8
> 2 VM 24909.25 NA 399.29 695.1 896.04
> 4 VM 17815.75 NA NA 742.78 950.63
> 8 VM 10216.25 NA NA NA 1002.81
>
>
> (and some more notes.... BOPS - business operations per second,
> TPS - transactions per second...
> SPECjbb tests CPU and Memory
> WebBench (the way we configured it) tests Network I/O and Disk I/O
>
> Values = AVG * VM count
> Domain configurations
> 1 VM - 1660 MB - SPECJBB 1500MB
> 2 VM - 1280 MB - SPECJBB - 1024MB
> 4 VM - 640 MB - SPECJBB - 512 MB
> 8 VM - 320 MB - SPECJBB - 256 MB
>
> Seeing how the SPECjbb numbers declined so bizarrely, I did
> some scheduling tests and found this out...
>
> Test1: Examine Xen's scheduling to determine if context
> switching is causing the overhead
> Period Slice BOPs
> Modified 8 VM 1 ms 125 us 6858
> 8 VM 10 ms 1.25 ms 14287
> 8 VM 100 ms 12.5 ms 18912
> 8 VM 1 Sec .125 Sec 20695
> 8 VM 2 Sec .25 Sec 21072
> 8 VM 10 Sec 1.25 Sec 21797
> 8 VM 100 Sec 12.5 Sec 11402
>
> I later learned that there was a period limit of 4 seconds,
> thus invalidating 10 and 100 seconds. However, this graph
> suggests that Xen needs some load and scheduling balancing done.
>
> I also did a memory test to determine if that could be the
> issue... I made a custom stream to run for a 2 minute period...
> and got these numbers
>
> Copy Scale Add Triad
> Host 3266.4 3215.47 3012.28 3021.79
> Modified 1 VM 3262.34 3220.34 3016.13 3025.28
>
>
> So we can see memory is not the issue...
>
> Now onto WebBench - After comparing the WebBench to the
> SPECjbb results, we get something interesting... NUMBERS
> increase as we increase the virtual machien count... So I would
> really like some idea on why this is. My understanding is
> this... When using the shared memory network drivers, there
> must be a local buffer, and when the buffer fills up, it puts
> the remaining into a global buffer, and when that fills up it
> puts it into a disk buffer? (These are all assumptions
> please correct me...) If that is the case is there an easy way
> to increase the local buffer to attempt to get better
> numbers? I also am looking into doing some tests that deal
> with multiple small transactions and 1 large transactions... I
> ran these all against a physical and image backed disk.
> Please any suggestions.
>
> (Note... I was running this on a 1 gigabit switch with only
> webbench running)...
>
> If there are any questions, I would be glad to respond.
>
> Thanks,
> David
>
>
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