Re: [Xen-devel] [PATCH v2 2/2] sched_credit2.c: runqueue_per_core code

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.03.15 at 11:03, <dario.faggioli@xxxxxxxxxx> wrote:
> OTOH, CPU_STARTING callbacks run:
>  - on the cpu being brought up;
>  - with interrupt disabled (see how the call to local_irq_enable(), in
>    start_secondary(), is *after* the invocation of
>    notify_cpu_starting()).
> 
> Here we are. And the reason why things works ok in Credit2, is that
> csched2_alloc_pdata() doesn't really allocate anything! In fact, in
> general, handling alloc_pdata() during CPU_STARTING would mean that we
> can't allocate any memory which, given the name of the function, would
> look rather odd. :-)
> 
> Nevertheless I see the value of doing so, and hence I think what we
> could do would be to introduce a new hook in the scheduler interface,
> called .init_pdata or .init_pcpu, and, in sched_*.c, split the
> allocation and the initialization parts. The former will be handled
> during CPU_UP_PREPARE, when allocation is possible, the latter during
> CPU_STARTING, when we have more info available to perform actual
> initializations.

Another alternative would be a new CPU_ALIVE (name subject to
change) notification after interrupts got enabled. That would (as
a follow-up cleanup) also allow the MTRR and microcode setup on
the CPU to no longer need explicit calls (which look reversed
anyway - surely we should update microcode before fiddling with
MTRRs).

Jan


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