Messages in this thread Patch in this message |  | | Subject | Re: sched_rt_period_timer causing large latencies | From | Mike Galbraith <> | Date | Thu, 05 Apr 2018 10:11:22 +0200 |
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On Thu, 2018-04-05 at 17:44 +1000, Nicholas Piggin wrote: > > > My method of dealing with the throttle beast from hell for ~big box RT > > is to stomp it flat during boot, as otherwise jitter is awful. > > How do you stomp it flat?
With a size 12 boot originally from SGI. Their extra hairy beasts tended to grind themselves to fine powder.
--- Documentation/admin-guide/kernel-parameters.txt | 2 ++ kernel/sched/core.c | 11 +++++++++++ 2 files changed, 13 insertions(+)
--- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2788,6 +2788,8 @@ noresume [SWSUSP] Disables resume and restores original swap space. + nortsched [KNL] Disables realtime task bandwidth control. + no-scroll [VGA] Disables scrollback. This is required for the Braillex ib80-piezo Braille reader made by F.H. Papenmeier (Germany). --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7091,3 +7091,14 @@ const u32 sched_prio_to_wmult[40] = { }; #undef CREATE_TRACE_POINTS + +/* + * Bootline option to disable sched_rt_runtime. + */ +static int __init parse_nortsched(char *arg) +{ + sysctl_sched_rt_runtime = -1; + return 0; +} +early_param("nortsched", parse_nortsched); + > If there could be some basic detection for throttling on a per-CPU > basis before invoking the best from hell, would that be possible to > move this out of normal paths?
It's one beast mauling the entire box, that's the problem. I just consider it a debugging tool, and turn it off (if it kicks in, the RT game was already over). RT disables RT group scheduling, so I don't have to care about that evilness.
> Alternatively I think most/all of the RT runtime is coming from > kernel threads, could they be exempted so this doesn't hit? Although > it would be sad to suddenly inflict these latencies on someone who > starts up an RT program :)
Yup, very sad. It should probably become percpu.
-Mike
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