linux-kernel - Re: [RFC][PATCH 00/32] Nohz cpusets v2 (adaptive tickless kernel)

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Message-ID: <CAOtvUMcH3AKRK9w832yFGY+JiebXb6P6jKM_H1Zcfjdp8+o32Q@mail.gmail.com>
Date:	Wed, 28 Mar 2012 08:47:15 +0200
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linaro-sched-sig@...ts.linaro.org,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Geoff Levand <geoff@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sven-Thorsten Dietrich <thebigcorporation@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Zen Lin <zen@...nhuawei.org>
Subject: Re: [RFC][PATCH 00/32] Nohz cpusets v2 (adaptive tickless kernel)

On Tue, Mar 27, 2012 at 6:22 PM, Christoph Lameter <cl@...ux.com> wrote:
> On Tue, 27 Mar 2012, Gilad Ben-Yossef wrote:
>
>> +static void vmstat_update(struct work_struct *w)
>> +{
>> +     int cpu, this_cpu = smp_processor_id();
>> +     int sleepy_cpu_counter = 0;
>> +     static spinlock_t lock;
>> +
>> +     if(spin_trylock(&lock)) {
>
> Trylock would cause cache bouncing between vmstat runs on various
> processors. The reason that vmstat_update exists is to avoid these cache
> bounces. Please no exclusive cacheline acquisiton by all cpus by default.
>

Right, I didn't think of that.

> The best method would be to assign a sacrifical lamb cpu and check if we
> are running on that cpu. That way taking a lock can be avoided.

Cool, I'll do it.

Thanks

Gilad


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Gilad Ben-Yossef
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