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

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Mon, 2016-03-14 at 02:37 -0600, Jan Beulich wrote:
> > 
> > > 
> > > > 
> > > > On 13.03.16 at 18:05, <lichong659@xxxxxxxxx> wrote:
> > So I still keep my design here?
> > 
> > Dario, Jan and Wei,
> Afaic:
> 
I agree almost on everything too.

About this:

> > 3) Use printk(XENLOG_G_WARNING ...) here, because of its rate limit
> > feature.
> I'd say XENLOG_G_DEBUG, and even that only if you really think
> the message is useful.
> 
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.

If we just print it once, I'd keep it G_WARNING.

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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