[PATCH 0 of 3] xen: sched_credit: fix tickling and add some tracing

[Dario Faggioli <raistlin@linux.it>]

Hello,

This small series deals with some weirdness in the mechanism with which the
credit scheduler choses what PCPU to tickle upon a VCPU wake-up.  Details are
available in the changelog of the first patch.

The new approach has been extensively benchmarked and proved itself either
beneficial or harmless. That means it does not introduce any significant amount
of overhead and/or performances regressions while, for some workloads, it
improves the performances quite sensibly (e.g., `sysbench --test=memory').

Full results in the first changelog too.

The rest of the series introduces some macros to enable generating
per-scheduler tracing events, retaining the possibility of distinguishing them,
even with more than one scheduler running at any given time (via cpupools), and
adds some tracing to the credit scheduler.

Thanks and Regards, Dario

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