Messages in this thread | | | Date | Wed, 2 Dec 2015 16:09:08 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/7] nohz: New tick dependency mask |
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On Wed, Dec 02, 2015 at 03:08:16PM +0100, Frederic Weisbecker wrote: > On Wed, Dec 02, 2015 at 11:56:33AM +0100, Peter Zijlstra wrote: > > On Tue, Dec 01, 2015 at 11:20:28PM +0100, Frederic Weisbecker wrote: > > > > > + prev = fetch_or(dep, BIT_MASK(bit)); > > > > > + if (!prev) { > > > > > + /* > > > > > + * We need the IPIs to be sent from sane process context. > > > > > > > > Why ? > > > > > > Because posix timers code is all called with interrupts disabled and we can't > > > send IPIs then. > > > > > > > > > > > > + * The posix cpu timers are always set with irqs disabled. > > > > > + */ > > > > > + schedule_work(&kick_all_work); > > > > > + } > > > > > +} > > > > > + > > > > > +/* > > > > > + * Set a global tick dependency. Lets do the wide IPI kick asynchronously > > > > > + * for callers with irqs disabled. > > > > > > > > This seems to suggest you can call this with IRQs disabled > > > > > > Ah right, that's a misleading comment. We need to use the _delayed() version > > > when interrupts are disabled. > > > > Why can't you use tick_nohz_full_kick_cpu() for all that, which is > > usable from IRQ context and avoid all that delayed muck? > > Because I need to kick all the CPUs where the task/signal is running on. That's > a bit difficult to do though. I think we had something to try to send an IPI to a task, > but I can't retrieve it. Looks easy to do anyway. But in the signal case I'd need to do > that for all tasks in the group. That sounds like a costly loop. > > So I simplify that with a global IPI.
Sure, but what I meant was that:
for_each_cpu(cpu, mask) tick_nohz_full_kick_cpu(cpu);
is IRQ safe, whereas the current thingy is not. Sure, its a wee bit less efficient, but do we really care?
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