From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Christoph Lameter <cl@linux.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Clark Williams <clark.williams@gmail.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Li Zefan <lizf@cn.fujitsu.com>, Ingo Molnar <mingo@kernel.org>,
Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH 00/32] [RFC] nohz/cpuset: Start discussions on nohz CPUs
Date: Fri, 2 Nov 2012 11:35:44 -0700 [thread overview]
Message-ID: <20121102183544.GZ3027@linux.vnet.ibm.com> (raw)
In-Reply-To: <0000013ac1a58555-bea33420-d101-4e86-abc5-11dd6863b7a8-000000@email.amazonses.com>
On Fri, Nov 02, 2012 at 03:03:01PM +0000, Christoph Lameter wrote:
> On Fri, 2 Nov 2012, Steven Rostedt wrote:
>
> > > also it would be best to sync this conceptually with the processors
> > > enabled for rcu processing.
> >
> > Processors can be disabled for rcu processing? Or are you talking about
> > Paul's new work of offloading rcu callbacks?
>
> Yes. Paul's new work to remove rcu processing from processors. That needs
> to be synced configuration wise somehow. It does not make sense to process
> rcu callbacks on processors where the timer tick does not work anymore.
In kernels built with CONFIG_FAST_NO_HZ=n, if there are callbacks,
then there will be a tick, with or without Frederic's adaptive ticks.
If CONFIG_FAST_NO_HZ=y, if there are callbacks but no tick, RCU will
arrange for a timer to allow RCU processing to proceed as needed, but
much longer than one tick in duration, and only until such time as the
RCU callbacks drain.
So, yes, people who need absolutely all jitter to be banished at whatever
cost would want both adaptive ticks and no-CBs CPUs, but not everyone
who wants adaptive ticks would necessarily want the burden of choosing
which CPUs get callbacks offloaded from and where they should be executed.
So I believe that these need to be controlled separately for the immediate
future.
Thanx, Paul
next prev parent reply other threads:[~2012-11-02 18:35 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-29 20:27 [PATCH 00/32] [RFC] nohz/cpuset: Start discussions on nohz CPUs Steven Rostedt
2012-10-29 20:27 ` [PATCH 01/32] nohz: Move nohz load balancer selection into idle logic Steven Rostedt
2012-10-30 8:32 ` Charles Wang
2012-10-30 15:39 ` Steven Rostedt
2012-10-29 20:27 ` [PATCH 02/32] cpuset: Set up interface for nohz flag Steven Rostedt
2012-10-30 17:16 ` Steven Rostedt
2012-10-29 20:27 ` [PATCH 03/32] nohz: Try not to give the timekeeping duty to an adaptive tickless cpu Steven Rostedt
2012-10-30 17:33 ` Steven Rostedt
2012-10-29 20:27 ` [PATCH 04/32] x86: New cpuset nohz irq vector Steven Rostedt
2012-10-30 17:39 ` Steven Rostedt
2012-10-30 23:51 ` Frederic Weisbecker
2012-10-31 0:07 ` Steven Rostedt
2012-10-31 0:45 ` Frederic Weisbecker
2012-10-29 20:27 ` [PATCH 05/32] nohz: Adaptive tick stop and restart on nohz cpuset Steven Rostedt
2012-10-30 18:23 ` Steven Rostedt
2012-10-29 20:27 ` [PATCH 06/32] nohz/cpuset: Dont turn off the tick if rcu needs it Steven Rostedt
2012-10-30 18:30 ` Steven Rostedt
2012-10-29 20:27 ` [PATCH 07/32] nohz/cpuset: Wake up adaptive nohz CPU when a timer gets enqueued Steven Rostedt
2012-10-29 20:27 ` [PATCH 08/32] nohz/cpuset: Dont stop the tick if posix cpu timers are running Steven Rostedt
2012-10-29 20:27 ` [PATCH 09/32] nohz/cpuset: Restart tick when nohz flag is cleared on cpuset Steven Rostedt
2012-10-30 18:55 ` Steven Rostedt
2012-10-29 20:27 ` [PATCH 10/32] nohz/cpuset: Restart the tick if printk needs it Steven Rostedt
2012-10-30 19:01 ` Steven Rostedt
2012-10-30 23:54 ` Frederic Weisbecker
2012-10-29 20:27 ` [PATCH 11/32] rcu: Restart the tick on non-responding adaptive nohz CPUs Steven Rostedt
2012-10-29 20:27 ` [PATCH 12/32] rcu: Restart tick if we enqueue a callback in a nohz/cpuset CPU Steven Rostedt
2012-10-29 20:27 ` [PATCH 13/32] nohz: Generalize tickless cpu time accounting Steven Rostedt
2012-10-29 20:27 ` [PATCH 14/32] nohz/cpuset: Account user and system times in adaptive nohz mode Steven Rostedt
2012-10-29 20:27 ` [PATCH 15/32] nohz/cpuset: New API to flush cputimes on nohz cpusets Steven Rostedt
2012-10-29 20:27 ` [PATCH 16/32] nohz/cpuset: Flush cputime on threads in nohz cpusets when waiting leader Steven Rostedt
2012-10-29 20:27 ` [PATCH 17/32] nohz/cpuset: Flush cputimes on procfs stat file read Steven Rostedt
2012-10-29 20:27 ` [PATCH 18/32] nohz/cpuset: Flush cputimes for getrusage() and times() syscalls Steven Rostedt
2012-10-29 20:27 ` [PATCH 19/32] x86: Syscall hooks for nohz cpusets Steven Rostedt
2012-10-29 20:27 ` [PATCH 20/32] nohz/cpuset: enable addition&removal of cpus while in adaptive nohz mode Steven Rostedt
2012-10-29 20:27 ` [PATCH 21/32] nohz: Dont restart the tick before scheduling to idle Steven Rostedt
2012-10-29 20:27 ` [PATCH 22/32] sched: Comment on rq->clock correctness in ttwu_do_wakeup() in nohz Steven Rostedt
2012-10-29 20:27 ` [PATCH 23/32] sched: Update rq clock on nohz CPU before migrating tasks Steven Rostedt
2012-10-29 20:27 ` [PATCH 24/32] sched: Update rq clock on nohz CPU before setting fair group shares Steven Rostedt
2012-10-29 20:27 ` [PATCH 25/32] sched: Update rq clock on tickless CPUs before calling check_preempt_curr() Steven Rostedt
2012-10-29 20:27 ` [PATCH 26/32] sched: Update rq clock earlier in unthrottle_cfs_rq Steven Rostedt
2012-10-29 20:27 ` [PATCH 27/32] sched: Update clock of nohz busiest rq before balancing Steven Rostedt
2012-10-29 20:27 ` [PATCH 28/32] sched: Update rq clock before idle balancing Steven Rostedt
2012-10-29 20:27 ` [PATCH 29/32] sched: Update nohz rq clock before searching busiest group on load balancing Steven Rostedt
2012-10-29 20:27 ` [PATCH 30/32] rcu: Switch to extended quiescent state in userspace from nohz cpuset Steven Rostedt
2012-10-29 20:27 ` [PATCH 31/32] nohz/cpuset: Disable under some configs Steven Rostedt
2012-10-29 20:27 ` [PATCH 32/32] nohz, not for merge: Add tickless tracing Steven Rostedt
2012-10-30 14:02 ` [PATCH 00/32] [RFC] nohz/cpuset: Start discussions on nohz CPUs Gilad Ben-Yossef
2012-11-02 14:23 ` Christoph Lameter
2012-11-02 14:37 ` Steven Rostedt
2012-11-02 14:50 ` David Nyström
2012-11-02 15:03 ` Christoph Lameter
2012-11-02 15:14 ` Steven Rostedt
2012-11-02 18:35 ` Paul E. McKenney [this message]
2012-11-02 20:16 ` Christoph Lameter
2012-11-02 20:41 ` Paul E. McKenney
2012-11-02 20:51 ` Steven Rostedt
2012-11-03 2:08 ` Paul E. McKenney
2012-11-05 15:17 ` Christoph Lameter
2012-11-05 22:41 ` Frederic Weisbecker
2012-11-05 22:32 ` Frederic Weisbecker
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