Date: Mon, 23 Jun 2014 17:39:34 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com,
        dipankar@in.ibm.com, akpm@linux-foundation.org,
        mathieu.desnoyers@efficios.com, josh@joshtriplett.org,
        tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org,
        dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com,
        fweisbec@gmail.com, oleg@redhat.com, ak@linux.intel.com, cl@gentwo.org,
        umgwanakikbuti@gmail.com
Subject: Re: [PATCH tip/core/rcu] Reduce overhead of cond_resched() checks
 for RCU
Message-ID: <20140624003934.GR4603@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <20140621025958.GA7185@linux.vnet.ibm.com>
 <53A85BF9.7030006@intel.com>
 <53A8611F.1000804@intel.com>
 <20140623180945.GL4603@linux.vnet.ibm.com>
 <53A8B884.6000600@intel.com>
 <20140624001519.GO4603@linux.vnet.ibm.com>
 <53A8C44E.7050000@intel.com>
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On Mon, Jun 23, 2014 at 05:20:30PM -0700, Dave Hansen wrote:
> On 06/23/2014 05:15 PM, Paul E. McKenney wrote:
> > Just out of curiosity, how many CPUs does your system have?  80?
> > If 160, looks like something bad is happening at 80.
> 
> 80 cores, 160 threads.  >80 processes/threads is where we start using
> the second thread on the cores.  The tasks are also pinned to
> hyperthread pairs, so they disturb each other, and the scheduler moves
> them between threads on occasion which causes extra noise.

OK, that could explain the near flattening of throughput near 80
processes.  Is 3.16.0-rc1-pf2 with the two RCU patches?  If so, is the
new sysfs parameter at its default value?

							Thanx, Paul

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