Messages in this thread | | | Date | Fri, 11 Jul 2014 13:35:13 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 11/17] rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs |
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On Fri, Jul 11, 2014 at 09:11:15PM +0200, Frederic Weisbecker wrote: > On Fri, Jul 11, 2014 at 02:05:08PM -0500, Christoph Lameter wrote: > > On Fri, 11 Jul 2014, Frederic Weisbecker wrote: > > > > > > That would imply that all no-nohz processors are housekeeping? So all > > > > processors with a tick are housekeeping? > > > > > > Well, now that I think about it again, I would really like to keep housekeeping > > > to CPU 0 when nohz_full= is passed. > > > > Yeah. > > > > > > Could we make that set configurable? Ideally I'd like to have the ability > > > > restrict the housekeeping to one processor. > > > > > > Ah, I'm curious about your usecase. But I think we can do that. And we should. > > > > The use case is pretty straightforward because we are trying to keep as > > much OS noise as possible off most processors. Processor 0 is the > > sacrificial lamb that will be used for all OS processing and hopefully all > > high latency operations will occur there. Processors 1-X have a tick but > > we still try to keep latencies sane. And then there is X-Y where tick is > > off. > > Ok. I don't entirely get why you need 1-X but I can easily imagine some non-latency-critical > stuff running there. > > Paul proposed "housekeeping=". If we ever go there, I'd rather vote for "sacrifical_lamb="
Given Christoph's desire for only one housekeeping CPU, I guess the counting version makes the most sense, so that "housekeeping=N" designates the first N non-nohz CPUs in numerical order as housekeeping CPUs. If there are fewer than N non-nohz CPUs, you get a splat at boot time and your request is capped at the number of non-nohz CPUs.
Seem reasonable?
Thanx, Paul
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