linux-kernel - Re: [patch 00/20] timer: Refactor the timer wheel

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Message-ID: <CANn89i+qVqbJWMZPhykqbti1tZSzG_vaiw+ippR--o1JCDfEGw@mail.gmail.com>
Date:	Mon, 13 Jun 2016 07:10:25 -0700
From:	Eric Dumazet <edumazet@...gle.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Chris Mason <clm@...com>,
	Arjan van de Ven <arjan@...radead.org>, rt@...utronix.de
Subject: Re: [patch 00/20] timer: Refactor the timer wheel

On Mon, Jun 13, 2016 at 1:40 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> The current timer wheel has some drawbacks:

...

> This series has also preparatory patches for changing the NOHZ timer handling
> from the current push to a pull model. Currently we decide at timer enqueue
> time on which cpu we queue the timer. This is exceptionally silly because
> there is no way to predict at enqueue time which cpu will be idle when the
> timer expires. Given the fact that most timers are canceled or rearmed before
> expiry this is even more silly. We trade a expensive decision and cross cpu
> access for a very doubtful benefit.
>

Also many TCP timers are armed from softirq handler interrupting idle task,
so scheduler believes current cpu is idle .

This patch series is really nice Thomas.