linux-kernel - [RFC PATCH 0/4] irq: Reorder time handling against HARDIRQ

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Message-Id: <20201125021542.30237-1-frederic@kernel.org>
Date:   Wed, 25 Nov 2020 03:15:38 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Heiko Carstens <hca@...ux.ibm.com>
Subject: [RFC PATCH 0/4] irq: Reorder time handling against HARDIRQ_OFFSET on IRQ entry

There are two issues with the current layout of tick_irq_enter() as
it's called before HARDIRQ_OFFSET is incremented:

1) It's not correctly handled by lockdep which doesn't consider it as
   hardirq context. And jiffies/timekeeping update take a few interesting
   locks.

2) Softirqs need to be explicitly disabled around it to prevent ksoftirqd
   from being spuriously woken up.

The current call dependency prevents tick_irq_enter() from being moved
after HARDIRQ_OFFSET: account_irq_enter_time() needs to be called before
HARDIRQ_OFFSET incrementation due to cputime index dispatch and it must
be called after tick_irq_enter() which updates the clocks that may be
necessary for cputime accounting.

Here is a proposal to fix this layout.

(The EXPORT_SYMBOL_GPL() in vtime will likely disappear in the next take
as they don't seem to be necessary anymore, but I'll need to check
that thoroughly).

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	irq/core

HEAD: 9502ee20aed8bb847176e1d7d83ccd0625430744

Frederic Weisbecker (4):
  sched/vtime: Consolidate IRQ time accounting
  s390/vtime: Convert to consolidated IRQ time accounting
  irqtime: Move irqtime entry accounting after irq offset incrementation
  irq: Call tick_irq_enter() inside HARDIRQ_OFFSET

 arch/ia64/kernel/time.c       | 22 +++++++---
 arch/powerpc/kernel/time.c    | 60 ++++++++++++++++++++--------
 arch/s390/include/asm/vtime.h |  1 -
 arch/s390/kernel/vtime.c      | 60 ++++++++++++++++++----------
 include/linux/hardirq.h       |  4 +-
 include/linux/vtime.h         | 18 ++++-----
 kernel/sched/cputime.c        | 75 +++++++++++++++++++++++++++--------
 kernel/softirq.c              | 16 +++-----
 8 files changed, 176 insertions(+), 80 deletions(-)

-- 
2.25.1