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From:   Frederic Weisbecker <frederic@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Anna-Maria Gleixner <anna-maria@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>
Subject: [RFC PATCH 00/10] timer: Reduce timers softirq (and other optimizations)
Date:   Wed,  1 Jul 2020 03:10:20 +0200
Message-Id: <20200701011030.14324-1-frederic@kernel.org>
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Juri Lelli has reported that threaded IRQs don't go along well with
full dynticks.

The tick never manages to stop due to the following endless loop:

* Timer tick raises timer softirq
* Ksoftirqd wakes up, restarts the tick (2 tasks in the runqueue)
* Timer tick raises timer softirq
* Ksoftirqd wakes up, etc...

The main issue here is that the tick fires the timer tick unconditionally,
whether timers have expired or not. This set is a proposal to lower that.

The 1st patch is actually a bugfix for a theoretical issue that I haven't
observed in practice. But who knows?

Patch 2 is a consolidation.

Patch 3 and 4 are optimizations.

The rest is about timer softirqs.

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	timers/softirq

HEAD: d0567dd5546d1f32eca3772a431488f8b0ac26a1

Thanks,
	Frederic
---

Frederic Weisbecker (10):
      timer: Prevent base->clk from moving backward
      timer: Move trigger_dyntick_cpu() to enqueue_timer()
      timer: Simplify LVL_START() and calc_index()
      timer: Optimize _next_timer_interrupt() level iteration
      timers: Always keep track of next expiry
      timer: Reuse next expiry cache after nohz exit
      timer: Expand clk forward logic beyond nohz
      timer: Spare timer softirq until next expiry
      timer: Remove must_forward_clk
      timer: Lower base clock forwarding threshold


 kernel/time/timer.c | 179 +++++++++++++++++++---------------------------------
 1 file changed, 64 insertions(+), 115 deletions(-)