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From: Thomas Gleixner <tglx@linutronix.de>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	viresh kumar <viresh.kumar@linaro.org>,
	Ingo Molnar <mingo@redhat.com>,
	linaro-kernel@lists.linaro.org,
	LKML <linux-kernel@vger.kernel.org>,
	Steven Miao <realmz6@gmail.com>,
	shashim@codeaurora.org, Frederic Weisbecker <fweisbec@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	cl@kernel.org
Subject: Re: [PATCH 1/2] timer: Avoid waking up an idle-core by migrate running timer
Date: Tue, 5 May 2015 15:00:41 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1505051459500.4225@nanos> (raw)
In-Reply-To: <1429987050.22254.187.camel@edumazet-glaptop2.roam.corp.google.com>

On Sat, 25 Apr 2015, Eric Dumazet wrote:
> On Thu, 2015-04-23 at 14:45 +0200, Thomas Gleixner wrote:
> 
> > You definitely have a point from the high throughput networking
> > perspective.
> > 
> > Though in a power optimizing scenario with minimal network traffic
> > this might be the wrong decision. We have to gather data from the
> > power maniacs whether this matters or not. The FULL_NO_HZ camp might
> > be pretty unhappy about the above.
> 
> Sure, I understand.
> 
> 
> To make this clear, here the profile on a moderately loaded TCP server,
> pushing ~20Gbits of data. Most of TCP output is ACK clock driven (thus
> from softirq context).
> 
> (using regular sendmsg() system calls, that why the
> get_nohz_timer_target() is 'only' second in the profile, but add the
> find_next_bit() to it and this is very close being at first position)
> 
> 
> 
>    PerfTop:    4712 irqs/sec  kernel:96.7%  exact:  0.0% [4000Hz cycles],  (all, 72 CPUs)
> -----------------------------------------------------------------------------------------
>     10.16%  [kernel]          [k] copy_user_enhanced_fast_string            
>      5.66%  [kernel]          [k] get_nohz_timer_target                     
>      5.59%  [kernel]          [k] _raw_spin_lock                            
>      2.53%  [kernel]          [k] __netif_receive_skb_core                  
>      2.27%  [kernel]          [k] find_next_bit                             
>      1.90%  [kernel]          [k] tcp_ack                                   
> 
> Maybe a reasonable heuristic would be to
> change /proc/sys/kernel/timer_migration default to 0 on hosts with more
> than 32 cpus.
> 
> profile with timer_migration = 0
> 
>    PerfTop:    3656 irqs/sec  kernel:94.3%  exact:  0.0% [4000Hz cycles],  (all, 72 CPUs)
> -----------------------------------------------------------------------------------------
>     13.95%  [kernel]          [k] copy_user_enhanced_fast_string            
>      4.65%  [kernel]          [k] _raw_spin_lock                            
>      2.57%  [kernel]          [k] __netif_receive_skb_core                  
>      2.33%  [kernel]          [k] tcp_ack               

Is that with the static key patch applied?

Thanks,

	tglx

  reply	other threads:[~2015-05-05 13:00 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-31  6:55 [PATCH 0/2] timer: Migrate running timers Viresh Kumar
2015-03-31  6:55 ` [PATCH 1/2] timer: Avoid waking up an idle-core by migrate running timer Viresh Kumar
2015-03-31 14:53   ` Peter Zijlstra
2015-04-14 23:13   ` Thomas Gleixner
2015-04-17  8:12     ` viresh kumar
2015-04-17  8:32       ` Ingo Molnar
2015-04-21 21:32       ` Thomas Gleixner
2015-04-21 21:54         ` Eric Dumazet
2015-04-22 15:29           ` Peter Zijlstra
2015-04-22 16:02             ` Eric Dumazet
2015-04-22 18:56               ` Thomas Gleixner
2015-04-22 19:59                 ` Eric Dumazet
2015-04-22 21:56                   ` Thomas Gleixner
2015-04-23  6:57                     ` Eric Dumazet
2015-04-23 12:45                       ` Thomas Gleixner
2015-04-25 18:37                         ` Eric Dumazet
2015-05-05 13:00                           ` Thomas Gleixner [this message]
2015-05-06 16:33                             ` Eric Dumazet
2015-04-15 15:54   ` Thomas Gleixner
2015-03-31  6:55 ` [PATCH 2/2] timer: Replace base-> 'running_timer' with 'busy' Viresh Kumar
2015-03-31 15:01 ` [PATCH 0/2] timer: Migrate running timers Viresh Kumar

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