Re: [PATCH tip/core/rcu] Reduce overhead of cond_resched() checks for RCU

From: Paul E. McKenney
Date: Mon Jun 23 2014 - 20:39:51 EST


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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