Messages in this thread | | | Date | Thu, 7 Nov 2013 23:54:10 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 2/4] irq_work: Provide a irq work that can be processed on any cpu |
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On Thu, Nov 07, 2013 at 11:50:34PM +0100, Jan Kara wrote: > On Thu 07-11-13 23:23:14, Frederic Weisbecker wrote: > > On Thu, Nov 07, 2013 at 11:19:04PM +0100, Jan Kara wrote: > > > On Thu 07-11-13 23:13:39, Frederic Weisbecker wrote: > > > > But then, who's going to process that work if every CPUs is idle? > > > Have a look into irq_work_queue(). There is: > > > /* > > > * If the work is not "lazy" or the tick is stopped, raise the irq > > > * work interrupt (if supported by the arch), otherwise, just wait > > > * for the next tick. We do this even for unbound work to make sure > > > * *some* CPU will be doing the work. > > > */ > > > if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) { > > > if (!this_cpu_cmpxchg(irq_work_raised, 0, 1)) > > > arch_irq_work_raise(); > > > } > > > > > > So we raise an interrupt if there would be no timer ticking (which is > > > what I suppose you mean by "CPU is idle"). That is nothing changed by my > > > patches... > > > > Ok but we raise that interrupt locally, not to the other CPUs. > True, but that doesn't really matter in this case. Any CPU (including the > local one) can handle the unbound work. So from the definition of the > unbound work things are OK.
I don't see how that can be ok. You want to offline a work because the local CPU can't handle it, right? If the local CPU can handle it you can just use local irq works.
> > Regarding my use for printk - if all (other) CPUs are idle then we can > easily afford making the current cpu busy printing, that's not a problem. > There's nothing else to do than to print what's remaining in the printk > buffer...
So if the current CPU can handle it, what is the problem?
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