[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20151120125441.GD17308@twins.programming.kicks-ass.net>
Date: Fri, 20 Nov 2015 13:54:41 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Morten Rasmussen <morten.rasmussen@....com>,
Arjan van de Ven <arjan@...ux.intel.com>,
Jacob Pan <jacob.jun.pan@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
John Stultz <john.stultz@...aro.org>,
LKML <linux-kernel@...r.kernel.org>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Len Brown <len.brown@...el.com>,
Rafael Wysocki <rafael.j.wysocki@...el.com>,
Eduardo Valentin <edubezval@...il.com>,
Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection
On Fri, Nov 20, 2015 at 11:58:12AM +0100, Thomas Gleixner wrote:
> That's not what I meant. If you don't want to control all that from
> the scheduler than you are back to that thread which "runs" at RT
> priority and does
>
> if (machine_on_fire) {
> defer_timer_interrupt(5ms);
> end = now + 5ms:
> while (now < end)
> mwait();
> }
>
> That's what the existing code does, but the above does not longer
> claim it's idle and confuses the hell out of nohz and whatever. It's
> just a "runaway" RT task which "hogs" the CPU for 5ms and makes the
> next timer interrupt firing late.
Right; so the naive way of implementing that is by simply programing the
timer hardware 5ms in the future and leaving it at that.
The problem with that would be a device interrupt happening and mucking
with timers, this would result in the timer hardware being reprogrammed
to a 'sane' value. I see two solutions for that:
- add another check in tick_program_event(); or,
- muck about with the evtdev pointer, such that we (temporarily) neuter
its clock_event_device::set_next_*() methods.
The later is fugly, but avoids any runtime overhead.
This all makes the idle-injection muck hard depend on hres_active, but I
think that's a sane constraint anyway.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists