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

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Message-ID: <20140515144553.GZ4570@linux.vnet.ibm.com>
Date:	Thu, 15 May 2014 07:45:53 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mike Galbraith <umgwanakikbuti@...il.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, 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...

							Thanx, Paul

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