linux-kernel - Re: [PATCH] sched/rt: don't try to balance rt

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Message-ID: <1400174841.18229.6.camel@marge.simpson.net>
Date:	Thu, 15 May 2014 19:27:21 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched/rt: don't try to balance rt_runtime when it is
 futile

On Thu, 2014-05-15 at 07:45 -0700, Paul E. McKenney wrote: 
> On Thu, May 15, 2014 at 05:18:51AM +0200, Mike Galbraith wrote:
> > On Wed, 2014-05-14 at 08:44 -0700, Paul E. McKenney wrote:
> > 
> > > In practice, not sure how much testing CONFIG_NO_HZ_FULL=y has received
> > > for -rt kernels in production environments.
> > 
> > I took 3.14-rt out for a quick spin on my 64 core box, it didn't work at
> > all with 60 cores isolated.  I didn't have time to rummage, but it looks
> > like there are still bugs to squash. 
> > 
> > Biggest problem with CONFIG_NO_HZ_FULL is the price tag.  It just raped
> > fast mover performance last time I measured.
> 
> I do have a report of the RCU grace-period kthreads (rcu_preempt,
> rcu_sched, and rcu_bh) consuming excessive CPU time on large boxes,
> but this is for workloads with lots of threads and context switches.
> 
> Whether relevant or not to your situation, working on it...

RCU signal was swamped by accounting.

-Mike

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