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Date: Wed, 28 Mar 2012 08:47:15 +0200
Message-ID: <CAOtvUMcH3AKRK9w832yFGY+JiebXb6P6jKM_H1Zcfjdp8+o32Q@mail.gmail.com>
Subject: Re: [RFC][PATCH 00/32] Nohz cpusets v2 (adaptive tickless kernel)
From: Gilad Ben-Yossef <gilad@benyossef.com>
To: Christoph Lameter <cl@linux.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>, linaro-sched-sig@lists.linaro.org,
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On Tue, Mar 27, 2012 at 6:22 PM, Christoph Lameter <cl@linux.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
Chief Coffee Drinker
gilad@benyossef.com
Israel Cell: +972-52-8260388
US Cell: +1-973-8260388
http://benyossef.com

"If you take a class in large-scale robotics, can you end up in a
situation where the homework eats your dog?"
 -- Jean-Baptiste Queru