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

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Message-ID: <20140115171037.GK31570@twins.programming.kicks-ass.net>
Date:	Wed, 15 Jan 2014 18:10:37 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	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,
	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

On Wed, Jan 15, 2014 at 06:03:10PM +0100, Oleg Nesterov wrote:
> On 01/14, Paul E. McKenney wrote:
> >
> > The __run_timers() function currently steps through the list one jiffy at
> > a time
> 
> And this is very suboptimal if jiffies - timer_jiffies is huge. Looks
> like, we should rework base->tv* structures, or (perhaps) optimize
> the "cascade" logic so that __run_timers() can increment timer_jiffies
> and move all the expired timers into work_list at one step. And the
> ->next_timer logic is obviously very suboptimal.

Thomas is actually actively working on a replacement for the entire
cascade mess.
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