Re: [PATCH v3 09/14] xen: sched: DOMCTL_*vcpuaffinity works with hard and soft affinity

[Dario Faggioli <dario.faggioli@citrix.com>]

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On lun, 2013-11-25 at 09:32 +0000, Jan Beulich wrote:
> >>> On 22.11.13 at 19:55, Dario Faggioli <dario.faggioli@citrix.com> wrote:
> > Therefore, I kept this interface as it was here, also considering that:
> >  - it's pretty late to re-re-redesign;
> >  - neither this nor the xc one are stable interfaces, so we can come
> >    back and revisit this later, if we want to.
> > 
> > Do you think this could be acceptable?
> 
> I wouldn't veto it, but I also dislike reduced flexibility when more
> flexibility is obviously achievable without much effort.
> 
Ok, understood. Ok, I'm up for changing this then. So, let m ask a few
questions, just to make sure ot get it right this time! ;-P

You are saying the interface should look as follows:

 int xc_vcpu_setaffinity(xc_interface *xch,
                         uint32_t domid,
                         int vcpu,
                         xc_cpumap_t cpumap_soft,
                         xc_cpumap_t cpumap_hard,
                         uint32_t flags);

Where both cpumap_soft and cpumap_hard are IN/OUT parameters and, as far
as OUT is concerned:
 - cpumap_hard will contain hard-affinity&online
 - cpumap_soft will contain what?
  (a) soft-affinity?
  (b) soft-affinity&online
  (c) soft-affinity&hard-affinity&online?

I would make it (c), as (a) is what xc_vcpu_setaffinity() retrieves,
while the '&online' part is particularly hard to get from other existing
calls (either at libxc and libxl level). Among (b) and (c), (c) is what
would be most useful for an high level caller (like libxl) to have it
ready, but it's also true that, if I give (b) to it, it could in theory
reconstruct (c) by himself (with the vice-versa not being true).

Thoughts?

Also, should I return something in either *only* of the maps when the
corresponding flag is set (and of course fill both when both flags are)?
Or do we always want to get something back (when non NULL, of course)
and apply the content of flag only to the IN path (i.e., for setting
either or both the afinities)?

Thanks and Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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