linux-kernel - Re: [PATCH tip/core/rcu] Reduce overhead of cond

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Date:	Tue, 24 Jun 2014 09:18:49 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	ak@...ux.intel.com, cl@...two.org, umgwanakikbuti@...il.com
Subject: Re: [PATCH tip/core/rcu] Reduce overhead of cond_resched() checks
 for RCU

On 06/23/2014 05:39 PM, Paul E. McKenney wrote:
> 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?

It's actually with _just_ e552592e03 applied on top of 3.16-rc1.

> If so, is the new sysfs parameter at its default value?

I didn't record that, and I've forgotten.  I'll re-run it to verify what
it was.
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