[Arm-dev] Gigabyte MP30-AR0

[Richard W.M. Jones]

On Tue, Mar 15, 2016 at 10:49:14PM +0000, Gordan Bobic wrote:
> On 2016-03-15 22:12, Richard W.M. Jones wrote:
> >On Tue, Mar 15, 2016 at 07:49:22PM +0000, Gordan Bobic wrote:
> >>On 2016-03-15 18:32, Richard W.M. Jones wrote:
> >>>I may be missing some context here, but is there some reason not to
> >>>just use a VM?
> >>
> >>Performance for one.
> >
> >Can you precisely quantify that?
> 
> On ARM? No, haven't tried it yet. On x86-64? Between 30% and 40%
> on a concurrent load saturating the CPU. Measured with different
> hypervisors (KVM, Xen and ESXi) and different generations of
> Intel CPUs from Core2 to Westmere Xeons. The results are reproducible
> on different loads, from a simple parallel kernel compile to a
> parallel read-only replay of MySQL general log.

You must be doing something very wrong if you see such a huge slowdown
with KVM.  Red Hat has a team that tracks performance and looks for
regressions between releases.  You shouldn't see more than a 5%
slowdown, except in rare and exceptional corner cases, or if it's
configured wrong.  Hard to say what - perhaps not using virtio, or not
using the right <cpu> model, or maybe overprovisioning.

> Here are some old results on Core2 class hardware:
> https://www.altechnative.net/2012/08/04/virtual-performance-part-1-vmware/

I can't comment on VMware, nor on results from 4 years ago.

> Unfortunately, later version of both hypervisors and hardware
> (I last ran similar tests using MySQL last year), exhibit the
> exact same performance degradation.
> 
> To reproduce:
> 1) 1 host, 1 VM
> 2) Give the VM all CPU cores available on the host
> 3) Run test with double the number of threads as there are CPU cores

So the problem is overprovisioning.

> >I think RHELSA 7.3 will have a 4.5 kernel.  Of course "LT" kernels
> >aren't really relevant for Red Hat, because we spend huge amounts of
> >money supporting our kernels long term.
> 
> Let's not go there:
> https://bugzilla.redhat.com/show_bug.cgi?id=773107

We don't support self-compiled kernels, for fairly obvious reasons.

Rich.

-- 
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