Re: [Xen-devel] [PATCH V4] xen/arm: domain_build: allocate lowmem for dom0 as much as possible

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

> For example, take a look at PVCalls which is entirely based on data
> copies:
>
> http://marc.info/?l=xen-devel&m=147639616310487
>
>
> I have already shown that it performs better than netfront/netback on
> x86 in this blog post:
>
> https://blog.xenproject.org/2016/08/30/pv-calls-a-new-paravirtualized-protocol-for-posix-syscalls/
>
>
> I have just run the numbers on ARM64 (APM m400) and it is still much
> faster than netfront/netback. This is what I get by running iperf -c in
> a VM and iperf -s in Dom0:
>
>         PVCalls             Netfront/Netback
> -P 1    9.9 gbit/s          4.53 gbit/s
> -P 2    17.4 gbit/s         5.57 gbit/s
> -P 4    24.36 gbit/s        5.34 gbit/s
>
> PVCalls is still significantly faster than Netfront/Netback.
This seems to be not a really fair comparison. And does not reflect
performance impact of the data copying itself.
Among all, our team is working on PV DRM implementation now. I guess
the first implementation would have a data copying, then we will
introduce a zero-copy. So it should be a good example to collect and
share impact numbers.

In embedded applications area, we are currently focused on, acceptable
performance drop, f.e. for io operations, is estimated as 3-5%
comparing to bare-metal system.

Anyway thank you for your comments, suggestions and examples.
I've got the point that we have to have solid reasoning baked with
pack of numbers to get something specific to us accepted by community.

Sincerely,
Andrii Anisov.

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