Messages in this thread | | | Date | Tue, 27 Mar 2012 11:13:39 -0500 (CDT) | From | Christoph Lameter <> | Subject | Re: [PATCH 11/32] nohz/cpuset: Don't turn off the tick if rcu needs it |
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On Tue, 27 Mar 2012, Frederic Weisbecker wrote:
> > Is there any way for userspace to know that the tick is not off yet due to > > this? It would make sense for us to have busy loop in user space that > > waits until the OS has completed all processing if that avoids future > > latencies for the application. > > What is the usecase you have in mind? Is it for realtime purpose?
Please do not use "realtime" since I am not sure what you mean by that. Its for a low latency applications that cannot use "realtime" because that implies high latencies.
> The "tick stopped" is a volatile and relative state.
The use case is an application that cannot tolerate the latencies introduced by timer tick processing. It will only start running when the system is in a sufficiently quiet state.
> Relative because if a timer list is enqueued to fire 1 second later, > the tick will be stopped until that happens. How do we consider this (common) > case? > > Also as Chris noted it is volatile because the tick can be restarted anytime > for random reasons: the CPU receives an IPI which makes it restart the > periodic tick.
Ok some sort of notification would be good for that case. If a timer tick happens and that was unavoidable then it would be good to log the reason why this occured so that the system can be configured in such a way that these interruptions are minimized.
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