linux-kernel - Re: Future of NOHZ full/isolation development (was Re: [NOHZ] Remove scheduler_tick_max

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Date:	Wed, 12 Nov 2014 11:41:09 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Tejun Heo <tj@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Mike Frysinger <vapier@...too.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@....qualcomm.com>,
	Hugh Dickins <hughd@...gle.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: Future of NOHZ full/isolation development (was Re: [NOHZ] Remove scheduler_tick_max_deferment)

On 11 November 2014 22:45, Frederic Weisbecker <fweisbec@...il.com> wrote:

> Here is a summarized list:
>
> * Unbound workqueues affinity (to housekeeper)
> * Unbound timers affinity (to housekeeper)
> * 1 Hz residual scheduler tick offlining to housekeeper
> * Fix some scheduler accounting that don't even work with 1 Hz: cpu load
>   accounting, rt_scale, load balancing, etc...
> * Lighten the syscall path and get rid of cputime accounting + RCU hooks
>   for people who want isolation + fast syscalls and faults.
> * Work on non-affinable workqueues
> * Work on non-affinable timers
> * ...

+ spurious interrupts with NOHZ_FULL on all architectures which break isolation
but doesn't get caught with traces. Can be observed with this:

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 481fa54..91d490d 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1244,7 +1244,8 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 {
        struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
        ktime_t expires_next, now, entry_time, delta;
-       int i, retries = 0;
+       int i, retries = 0, count = 0;
+       static int total_spurious;

        BUG_ON(!cpu_base->hres_active);
        cpu_base->nr_events++;
@@ -1304,10 +1305,14 @@ void hrtimer_interrupt(struct clock_event_device *dev)
                                break;
                        }

+                       count++;
                        __run_hrtimer(timer, &basenow);
                }
        }

+       if (!count)
+               pr_err("____%s: Totalspurious: %d\n", __func__,
++total_spurious);
+
        /*
         * Store the new expiry value so the migration code can verify
         * against it.
--
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