On 14-05-14 10:49 PM, Mike Galbraith wrote: > On Wed, 2014-05-14 at 15:11 -0400, Paul Gortmaker wrote: > >> Given that, perhaps a separate change to sched_rt_runtime_exceeded() >> that works out the CPU from the rt_rq, and returns zero if it is a >> nohz_full cpu? Does that make sense? Then the nohz_full people won't >> get the throttling message even if they go 100%. > > I don't get it. What reason would there be to run a hog on a dedicated > core as realtime policy/priority? Given no competition, there's nothing > to prioritize, you could just as well run a critical task as SCHED_IDLE. Well, as per the original commit log, we acknowledge that people will do stupid things that don't make 100% sense, and when they do, we should ideally behave in a sane fashion in response to that. And I don't think that "no competition" is a given for most folks. They see all these internal threads running and just figure they can chrt their way to a solution, vs. taking the time to clean up, enable RCU_NOCB etc etc. Don't get me wrong; I'm not defending such behaviour... > > I would also expect that anyone wanting bare metal will have all of > their critical cores isolated from the scheduler, watchdogs turned off > as well as that noisy throttle, the whole point being to make as much > silent as possible. Seems to me tick_nohz_full_cpu(cpu) should be > predicated by that cpu being isolated from the #1 noise source, the > scheduler and its load balancing. There's just no point to nohz_full > without that, or if there is, I sure don't see it. An interesting point. One could argue that the default for the nohz_full cores should be to be isolated from the scheduler, vs needing to be manually excluded. P. -- > > When I see people trying to run a hog as a realtime task, it's because > they are trying in vain to keep competition away from precious cores.. > and one mlockall with a realtime hog blocking flush_work() gives them a > wakeup call. > > -Mike > -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
