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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.03.16 at 10:10, <dario.faggioli@xxxxxxxxxx> wrote:
> On Mon, 2016-03-14 at 02:37 -0600, Jan Beulich wrote:
>> > > > On 13.03.16 at 18:05, <lichong659@xxxxxxxxx> wrote:
> 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.

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.

Jan


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