Messages in this thread | | | Date | Fri, 11 Jul 2014 22:45:05 +0200 | From | Frederic Weisbecker <> | 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 01:35:13PM -0700, Paul E. McKenney wrote: > 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?
I wonder if it's wouldn't be rather reasonable to affine housekeeping to all non-nohz-full CPUs by default and then people who want finergrained housekeeping can affine manually kthreads from userspace.
That implies to bind without PF_NO_SETAFFINIT but that's easy enough to do.
> > Thanx, Paul >
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