Re: [Xen-devel] crash in csched_load_balance after xl vcpu-pin

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Tue, 2018-04-10 at 21:03 +0200, Olaf Hering wrote:
> On Tue, Apr 10, Dario Faggioli wrote:
> 
> > As said, its cpus= and cpus_soft=, and you probably just need
> > cpus="node:1"
> > cpus_soft="node:1"
> > Or, even just:
> > cpus="node:1"
> > as, if soft-affinity is set to be equal to hard, it is just
> > ignored.
> 
> Well, that was a noop. But xl.cfg states "nodes:0-3,^node:2", so this
> should work:
> cpus="nodes:3,^node:0"
> cpus_soft="nodes:3,^node:0"
> 
Well, but "nodes:0-3,^node:2" is a way to say that you want nodes 0, 1
and 3. I.e., you are defining a set made up of 0,1,2,3, and then you
remove 2.

With "nodes:3,^node:0", you're saying that you want node 3, but not
node 0. I.e., basically, you are creating a set with 3 in it, and then
trying to remove 0... I agree this is not technically wrong, but it
does not make much sense. Why you're not using
"node:3,^node:0,^node:1,^node:2" then?

So, really, the way to achieve what you seem to me to be wanting to
achieve is:

cpus="node:3"

All that being said, yes, "nodes:3,^node:0" should work (and behave
exactly as "node:3" :-) ).

And in fact...

> xl create -f fv_sles12sp1.f.tst.cfg
>
... parsing, at the xl level, worked, or xl itself would have errored
out, with its own message.

> libxl: error: libxl_sched.c:62:libxl__set_vcpuaffinity: Domain
> 16:Setting vcpu affinity: Invalid argument
> libxl: error: libxl_dom.c:461:libxl__build_pre: setting affinity
> failed on vcpu `0'
>
This is xc_vcpu_setaffinity() failing with EINVAL, in
libxl__set_vcpuaffinity().

> Same for nodes:2..., just nodes:1... works.
> 
> And after some attempts, cpus="nodes:2/3" fails too.
>
"nodes:2/3" is not supported.

> There is no indication what is invalid.
> 
Mmm... I seem to recall having tested the parser against various corner
cases and/or ill-defined input. Still, my guess is that using ^ like
that (i.e., excluding something which was not there in the first
place), may result in a weird/corrupted cpumask.

If that is the case, it indeed would be a bug. I'll check the code
tomorrow.

In the meanwhile --let me repeat myself-- just go ahead with "node:2",
"node:3", etc. :-D

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Software Engineer @ SUSE https://www.suse.com/

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