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Re: [Xen-devel] [PATCH v6 for Xen 4.7 1/4] xen: enable per-VCPU parameter settings for RTDS scheduler

On Mon, 2016-03-14 at 03:15 -0600, Jan Beulich wrote:
> > > > On 14.03.16 at 10:10, <dario.faggioli@xxxxxxxxxx> wrote:
> > I think it has some value to have this in the logs. In fact,
> > someone
> > that ended up with small values --either by bug/chance, or in
> > general
> > without a specific need for them-- and is seeing
> > performance/scheduling
> > issues will still be able to find this.
> > 
> > And printing it somewhere else than in Xen is impractical (see my
> > reply
> > to Wei).
> > 
> > However, we may well print it just once, as soon as the first vcpu
> > with
> > potentially problematic parameters is hit, and then silence it.
> > 
> > Linux has things like WARN_ON_ONCE to do this:
> > http://lxr.free-electrons.com/source/include/asm-generic/bug.h#L109
> >  
> > 
> > I don't see anything like it in Xen, so you'd need to either
> > implement
> > it, or arrange for something with the same effect locally.
> One of the reasons we don't (yet) have this is because commonly
> (like is the case here) printing such once globally isn't really what
> you want - you'd much rather see it once per domain.
Ah, I did not know that was part of the reason, but it makes sense.

However, for this specific case, I was also considering that, and I
agree, if possible/not to difficult to implement, once per domain would
indeed be better.

<<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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