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Message-ID: <8f0763efd927f791b1c13ca65712a2380985297a.camel@redhat.com>
Subject: Re: [PATCH 1/4] tick/sched: Forward timer even in nohz mode
From:   Scott Wood <swood@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>
Cc:     linux-kernel@vger.kernel.org
Date:   Mon, 06 Jan 2020 14:12:19 -0600
In-Reply-To: <1576538545-13274-1-git-send-email-swood@redhat.com>
References: <1576538545-13274-1-git-send-email-swood@redhat.com>
Organization: Red Hat
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On Mon, 2019-12-16 at 18:22 -0500, Scott Wood wrote:
> Currently when exiting nohz, the expiry will be forwarded as if we
> had just run the timer.  If we re-enter nohz before this new expiry,
> and exit after, this forwarding will happen again.  If this load pattern
> recurs the tick can be indefinitely postponed.
> 
> To avoid this, use last_tick as-is rather than calling hrtimer_forward().
> However, in some cases the tick *will* have just run (despite being
> "stopped"), and leading to double timer execution.
> 
> To avoid that, forward the timer after every tick (regardless of nohz
> status) and keep last_tick up-to-date.  During nohz, last_tick will
> reflect what the expiry would have been if not in nohz mode.
> 
> Signed-off-by: Scott Wood <swood@redhat.com>
> ---
>  kernel/time/tick-sched.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)

Any comments on these patches?

Thanks,
Scott