Messages in this thread | | | Date | Thu, 6 Apr 2017 13:56:12 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU mask |
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On Thu, 6 Apr 2017, Peter Zijlstra wrote: > On Thu, Apr 06, 2017 at 01:03:16PM +0200, Thomas Gleixner wrote: > > > Fair enough, but I prefer to have the ability for a temporary restriction > > of the user space visible cpus allowed mask in the core code, which can be > > used for both migrate_disable() and things like that MIPS FPU stuff rather > > than all those home brewn hackeries which are prone to bitrot, security > > issues and subtle wreckage. cpus_allowed should be solely under sched core > > control and not accessible from anything outside. > > So the big difference between what MIPS does and what migrate_disable() > needs here is the amount of storage. > > For migrate_disable() we don't need a whole second cpumask bitmap. We > can simply use one of the static cpumask_of() things. > > Given that cpumask bitmaps can be quite large, adding another one to > task_struct just for $very_rare_occasion, doesn't seem like a good > thing.
A pointer to the effective mask is definitely enough. And that's what we need for migrate_disable() as well. That still leaves the storage requirement to MIPS.
Thanks,
tglx
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