Messages in this thread | | | Date | Tue, 27 Mar 2012 20:19:15 -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, Steven Rostedt wrote:
> > Obviously compiling a kernel with preemptiong introduces additional > > overhead to guarantee more deterministic behavior. Additional overhead > > increases latencies generated by the OS in general. Compile a kernel > > without preemption and it will run faster and thus have lower latencies. > > I call that "lower overhead".
Good marketing but it does not change the facts.
> "Latency is a measure of time delay experienced in a system, the precise > definition of which depends on the system and the time being measured. > Latencies may have different meaning in different contexts." > > That last sentence is key. So lets avoid the term "latency" as it > obviously has a different meaning to the both of us. > > Instead, lets use "determinism" (what we call latency in the realtime > world) and "overhead" (what you seem to see as latency caused by the > kernel).
I sure wish you would be using the term determinism instead of "latency".
Overhead causes latency and the definition that you quoted is what I am talking about. Latencies are the delays in processing experienced by the application through the speed of system calls and by interruptions of a user space process by the kernel for various reasons.
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