Re: [Xen-devel] [PATCH 15/16] xen: sched: scratch space for cpumasks on Credit2

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 18/03/16 19:06, Dario Faggioli wrote:
> like what's there already in both Credit1 and RTDS. In
> fact, when playing with affinity, a lot of cpumask
> manipulation is necessary, inside of various functions.
>
> To avoid having a lot of cpumask_var_t on the stack,
> this patch introduces a global scratch area.
>
> Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> ---
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> ---

I would suggest instead going with

static DEFINE_PER_CPU(cpumask_t, csched2_cpumask_scratch);

Functions which want to use it can use

cpumask_t *scratch = &this_cpu(csched2_cpumask_scratch);


This avoids all this opencoded allocation/refcounting, the chance that
starting a scheduler would fail for memory reasons, and one extra
cpumask in the per-cpu data area won't break the bank.

~Andrew

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