From: Arjan van de Ven <arjan@linux.intel.com>
To: Mike Galbraith <efault@gmx.de>
Cc: RT <linux-rt-users@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch] clockevents: Reinstate the per cpu tick skew
Date: Wed, 28 Dec 2011 14:35:36 +0100 [thread overview]
Message-ID: <4EFB1B28.7090203@linux.intel.com> (raw)
In-Reply-To: <1325049448.4726.16.camel@marge.simson.net>
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On 12/28/2011 6:17 AM, Mike Galbraith wrote:
> On Tue, 2011-12-27 at 10:20 +0100, Mike Galbraith wrote:
>> Quoting removal commit af5ab277ded04bd9bc6b048c5a2f0e7d70ef0867
>> Historically, Linux has tried to make the regular timer tick on
>> the various CPUs not happen at the same time, to avoid contention
>> on xtime_lock.
>>
>> Nowadays, with the tickless kernel, this contention no longer
>> happens since time keeping and updating are done differently. In
>> addition, this skew is actually hurting power consumption in a
>> measurable way on many-core systems. End quote
>
> Hm, nohz enabled, hogs burning up 60 of 64 cores.
>
> 56.11% [kernel] [k] ktime_get 5.54% [kernel] [k]
> scheduler_tick 4.02% [kernel] [k] cpuacct_charge 3.78%
> [kernel] [k] __rcu_pending 3.76% [kernel] [k]
> tick_sched_timer 3.42% [kernel] [k] native_write_msr_safe
> 1.58% [kernel] [k] run_timer_softirq 1.28% [kernel] [k]
> __schedule 1.21% [kernel] [k] apic_timer_interrupt 1.07%
> [kernel] [k] _raw_spin_lock 0.81% [kernel] [k]
> __switch_to 0.67% [kernel] [k] thread_return
>
> Maybe skew-me wants to become a boot option?
this is 56% of kernel time.. of how much total time?
(and are you using a system where tsc/lapic can be used, or are you
using one of those boatanchors that need hpet?)
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next prev parent reply other threads:[~2011-12-28 13:35 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-24 9:06 3.0.14-rt31 + 64 cores = very bad jitter == highly synchronized tick? Mike Galbraith
2011-12-25 7:31 ` Mike Galbraith
2011-12-26 8:04 ` Mike Galbraith
2011-12-27 6:40 ` Mike Galbraith
2011-12-27 9:20 ` [patch] clockevents: Reinstate the per cpu tick skew Mike Galbraith
2011-12-28 5:17 ` Mike Galbraith
2011-12-28 8:22 ` Mike Galbraith
2011-12-28 9:59 ` Mike Galbraith
2011-12-28 13:35 ` Arjan van de Ven [this message]
2011-12-28 14:59 ` Mike Galbraith
2011-12-28 16:57 ` Peter Zijlstra
2011-12-28 17:28 ` Mike Galbraith
2011-12-29 7:22 ` Mike Galbraith
2011-12-28 13:32 ` Arjan van de Ven
2011-12-28 15:10 ` Mike Galbraith
2012-01-03 6:20 ` Mike Galbraith
2012-04-23 6:13 ` irq latency regression post af5ab277 - was " Mike Galbraith
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