Messages in this thread | | | Date | Thu, 16 May 2013 19:57:14 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/2] nohz: Disable LOCKUP_DETECTOR when NO_HZ_FULL is enabled |
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On Thu, May 16, 2013 at 01:38:12PM +0200, Frederic Weisbecker wrote: > On Thu, May 16, 2013 at 10:10:27AM +0200, Peter Zijlstra wrote: > > On Wed, May 15, 2013 at 01:04:01PM -0400, Steven Rostedt wrote: > > > On Wed, 2013-05-15 at 18:59 +0200, Peter Zijlstra wrote: > > > > > > > At which point we could run the watchdog without perf_event_task_tick(). > > > > > > At which point we can drop the disable LOCKUP_DETECTOR when NO_HZ_FULL > > > is enabled ;-) > > > > > > > Can we? The thing I'm worried about is RCU (of course!). ISTR we rely on RCU > > working in NMI context. AFAIR for RCU to work, we need to come out of out magic > > NO_HZ state since that would've put RCU into EQS. > > > > Frederic, PaulMck? > > But they are protected inside rcu_nmi_*() functions, that's the only thing we need. > If this interrupt userspace then we resume back to it quickly after the NMI and > re-enter EQS. > > No need to restart the tick for that. A remote CPU that wants a quiescent state > from the dyntick CPU will notice soon enough the EQS.
Right.. I just wasn't sure how much damage the RCU EQS stop/(re)start did to the entire NO_HZ_FULL situation.
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