Re: Xen I/O performance

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

Matthias Scheler wrote:
>         Hello,
>
> in the past NetBSD Xen was often blamed to cause a massive loss of
> I/O performance on the dom0 compared to a machine not using Xen.
> In my attempt to evaluate NetBSD Xen for use on my new server at
> home I've run two benchmarks:
>
> 1.) Extracting all the NetBSD 4.0 release source sets (located on a
>     tmpfs) to at the same empty local filesystem using "tar"
>
> 2.) Copying 32GB from "/dev/zero" to a file on the same non-empty
>     filesystem using "dd".
>
> The machine used for the test is a Xeon 3040 (Core 2 Duo architecture,
> 1.87GHz, two cores) with 5GB memory and a single 160GB SATA harddisks.
> I've used the 4.99.63 NetBSD-amd64 GENERIC and XEN3_DOM0 kernels. The
> amd64 kernel could use two CPU cores and 5GB memory, the Xen kernel
> only one CPU core and 3.5GB memory.
>
> Here are the results:
>
> Kernel          "tar" (time in minutes)               "dd" (throughput in 
> bytes/sec)
> GENERIC         4:19.31                         46391830
> XEN3_DOM0       3:59.20                         47161618
>
> I'm impressed. The Xen kernel did much better than I expected.
> Congratulations to Manuel for with excellent work.

There's potential for even better results.
When libc uses "call" instead of "syscall" when running in a Xen 
environment (Dom0 or DomU), then there's some speedup because
that would save the intervention of the hypervisor.

Christoph