linux-kernel - Re: [PATCH tip/core/timers 2/4] timers: Reduce __run

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Message-ID: <20140115173858.GC14473@redhat.com>
Date:	Wed, 15 Jan 2014 18:38:58 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu
Subject: Re: [PATCH tip/core/timers 2/4] timers: Reduce __run_timers()
	latency for empty list

forgot to mention...

On 01/14, Paul E. McKenney wrote:
>
> +static bool catchup_timer_jiffies(struct tvec_base *base)
> +{
> +#ifdef CONFIG_NO_HZ_FULL
> +	if (!base->all_timers) {
> +		base->timer_jiffies = jiffies;
> +		return 1;
> +	}
> +#endif /* #ifdef CONFIG_NO_HZ_FULL */
> +	return 0;
> +}

Do we really want ifdef?

This check is cheap, and !CONFIG_NO_HZ_FULL case looks a bit
strange because we still update ->all_timers for no reason.

Oleg.

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