linux-kernel - [PATCH 00/25] hrtimer: Provide softirq context hrtimers

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Date:   Thu, 31 Aug 2017 12:23:33 -0000
From:   Anna-Maria Gleixner <anna-maria@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Christoph Hellwig <hch@....org>, keescook@...omium.org,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 00/25] hrtimer: Provide softirq context hrtimers

There are quite some places in the kernel which use a combination of
hrtimers and tasklets to make use of the precise expiry of hrtimers, which
schedule a tasklet to bring the actual function into softirq context.

This was introduced when the previous hrtimer softirq code was
removed. That code was implemented by expiring the timer in hard irq
context and then deferring the execution of the callback into softirq
context. That caused a lot of pointless shuffling between the rbtree and a
linked list.

In recent discussions it turned out that more potential users of hrtimers
in softirq context might come up. Aside of that the RT patches need this
functionality as well to defer hrtimers into softirq context if their
callbacks are not interrupt safe on RT.

This series implements a new approach by adding SOFT_* clock ids and
instead of doing the list shuffle, timers started with these clock ids are
put into separate soft expiry hrtimer queues. These queues are evaluated
only when the hardirq context detects that the first expiring timer in the
softirq queues has expired. That makes the overhead in the hardirq context
minimal.

The series reworks the code to reuse as much as possible from the existing
facilities for the new softirq hrtimers and integrates them with all
flavours of hrtimers (HIGH_RES=y/n - NOHZ=y/n).

To achieve this quite some of the conditionals in the existing code are
removed for the price of adding some pointless data and state tracking to
the HIGH_RES=n case. That's minimal, but well worth it as it increases the
readability and maintainability of the code.

The first part of the series implements the new functionality and the
second part converts the hrtimer/tasklet users to make use of it and
removes struct hrtimer_tasklet and the surrounding helper functions.

This series is available from git as well:

    git://git.kernel.org/pub/scm/linux/kernel/git/bigeasy/linux-hrtimer.git soft_hrtimer
    https://git.kernel.org/bigeasy/linux-hrtimer/h/soft_hrtimer

Thanks,

	Anna-Maria

---
 drivers/net/usb/cdc_ncm.c             |   37 +-
 drivers/net/wireless/mac80211_hwsim.c |   44 +-
 drivers/usb/gadget/function/f_ncm.c   |   28 -
 include/linux/hrtimer.h               |   76 ++---
 include/linux/interrupt.h             |   25 -
 include/linux/usb/cdc_ncm.h           |    2 
 include/net/xfrm.h                    |    2 
 kernel/softirq.c                      |   51 ---
 kernel/time/hrtimer.c                 |  513 +++++++++++++++++++++-------------
 net/can/bcm.c                         |  150 +++------
 net/xfrm/xfrm_state.c                 |   29 +
 sound/drivers/dummy.c                 |   16 -
 12 files changed, 484 insertions(+), 489 deletions(-)