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Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU mask

From Thomas Gleixner <tglx@linutronix.de>
Newsgroups linux.kernel
Subject Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU mask
Date 2017-04-06 14:00 +0200
Message-ID <ttef0-81k-23@gated-at.bofh.it> (permalink)
References (3 earlier) <ttcZA-7iO-21@gated-at.bofh.it> <ttd9g-7m3-11@gated-at.bofh.it> <ttdiV-7pf-1@gated-at.bofh.it> <ttdsC-7HU-11@gated-at.bofh.it> <tteeZ-81k-13@gated-at.bofh.it>
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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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Thread

[RFC PATCH] kernel: sched: Provide a pointer to the valid CPU mask Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-04-04 20:50 +0200
  Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Ingo Molnar <mingo@kernel.org> - 2017-04-05 09:40 +0200
    Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-04-05 10:40 +0200
      Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Ingo Molnar <mingo@kernel.org> - 2017-04-06 08:20 +0200
        Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-04-06 09:40 +0200
          Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Ingo Molnar <mingo@kernel.org> - 2017-04-06 10:10 +0200
            Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-04-06 11:30 +0200
              Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 11:50 +0200
                Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Thomas Gleixner <tglx@linutronix.de> - 2017-04-06 13:00 +0200
                Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 13:50 +0200
            Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 11:40 +0200
              Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 11:50 +0200
            Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Thomas Gleixner <tglx@linutronix.de> - 2017-04-06 12:40 +0200
              Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Ingo Molnar <mingo@kernel.org> - 2017-04-06 13:10 +0200
                Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Thomas Gleixner <tglx@linutronix.de> - 2017-04-06 13:20 +0200
                Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Ingo Molnar <mingo@kernel.org> - 2017-04-07 09:20 +0200
    Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 11:40 +0200
  Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 11:40 +0200
    Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-04-06 11:50 +0200
      Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 12:40 +0200
        Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Thomas Gleixner <tglx@linutronix.de> - 2017-04-06 12:50 +0200
          Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 13:00 +0200
            Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Thomas Gleixner <tglx@linutronix.de> - 2017-04-06 13:10 +0200
              Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 14:00 +0200
                Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Thomas Gleixner <tglx@linutronix.de> - 2017-04-06 14:00 +0200
                Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU  mask Peter Zijlstra <peterz@infradead.org> - 2017-04-06 14:40 +0200

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