Re: [Xen-devel] [PATCH 3 of 3] libxl: make it possible to explicitly specify default sched params

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-05-24 at 14:57 +0100, Ian Jackson wrote:
> George Dunlap writes ("Re: [Xen-devel] [PATCH 3 of 3] libxl: make it possible 
> to explicitly specify default sched params"):
> >    This might be nice; but we're
> > implicitly baking in an assumption that parameters with the same name
> > have to have roughly similar meanings across all schedulers.
> 
> We can make this assumption true in the libxl API even if it's false
> at the Xen level, simply by renaming parameters which have
> "sufficiently" divergent semantics.
> 
> > Furthermore, if someone sets a "cap" in the config file, for example,
> > but starts the VM in a pool running credit2, should we really just
> > silently ignore it, or should we alert the user in some way?
> 
> We don't currently have any way to warn anyone about unused parameter
> settings in xl config files.

Warning about known parameters which don't effect the current scheduler
should be pretty easy to do though.

> 
> > But I think whichever way we choose, we should take it to its logical
> > conclusion.  Which in the "One Struct" way, would mean having a single
> > domain_get/domain_set function, and in the "separate struct" way would
> > probably mean specifying the scheduler -- i.e., "credit_weight",
> > "credit2_weight" or something like that.  (Obviously we need xm
> > compatibility, but we can throw a warning to encourage people to
> > change their config files.)
> 
> Yes.
> 
> Ian.



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