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From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, mingo@kernel.org,
	jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, dhowells@redhat.com,
	edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com,
	joel.opensrc@gmail.com
Subject: Re: [PATCH tip/core/rcu 01/22] sched: Make non-production PREEMPT cond_resched() help Tasks RCU
Date: Mon, 23 Apr 2018 09:47:42 -0400	[thread overview]
Message-ID: <20180423094742.6582e19d@gandalf.local.home> (raw)
In-Reply-To: <20180423124000.GL26088@linux.vnet.ibm.com>

On Mon, 23 Apr 2018 05:40:00 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> > I'm confused.. why is having this conditional on TRACEPOINT_BENCHMARK a
> > sane idea?  
> 
> Because the TRACEPOINT_BENCHMARK tests are insane, so a similar
> level of insanity is required to make things work.  Plus having this
> be unconditional would not be good for performance, as 0day has been
> telling me frequently over the past couple of years.

Just for some context. The tracepoint benchmark (which should never be
enabled in any production machine), will start a thread when the
benchmark trace event is enabled. This thread will never exit (until
the trace event is disabled), and does a benchmark loop and constantly
calls "cond_resched()" to allow other tasks to run. The point is, this
thread will never have a quiescent state for task_rcu, unless we tell
rcu that cond_resched() is a quiescent state. But this is only required
because the tracepoint benchmark has this nasty thread, that is only
used for debugging and benchmarking the tracepoint (during development).

I also suggested having a direct call into RCU from the thread to tell
RCU that it entered a quiescent state, but Paul didn't like that idea
as it caused the tracepoint benchmark to call too deep into RCU
internals.

 http://lkml.kernel.org/r/20180227153646.GD3777@linux.vnet.ibm.com


-- Steve

  reply	other threads:[~2018-04-23 13:47 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-23  2:31 [PATCH tip/core/rcu 0/22] Miscellaneous fixes for v4.18 Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 01/22] sched: Make non-production PREEMPT cond_resched() help Tasks RCU Paul E. McKenney
2018-04-23  8:51   ` Peter Zijlstra
2018-04-23 12:40     ` Paul E. McKenney
2018-04-23 13:47       ` Steven Rostedt [this message]
2018-04-23 14:10         ` Peter Zijlstra
2018-04-23 14:35           ` Steven Rostedt
2018-04-23 15:47             ` Paul E. McKenney
2018-04-23 19:12               ` Paul E. McKenney
2018-04-23 14:03       ` Peter Zijlstra
2018-04-23  2:32 ` [PATCH tip/core/rcu 02/22] rcu: Inline rcu_preempt_do_callback() into its sole caller Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 03/22] rcu: Don't allocate rcu_nocb_mask if no one needs it Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 04/22] rcu: Call wake_nocb_leader_defer() with 'FORCE' when nocb_q_count is high Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 05/22] rcu: Remove deprecated RCU debugfs tracing code Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 06/22] rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs() Paul E. McKenney
2018-04-23  8:53   ` Peter Zijlstra
2018-04-23 12:32     ` Paul E. McKenney
2018-04-23 12:48       ` Peter Zijlstra
2018-04-23 13:12         ` Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 07/22] softirq: Eliminate unused cond_resched_softirq() macro Paul E. McKenney
2018-04-23  8:54   ` Peter Zijlstra
2018-04-23 13:25     ` Eric Dumazet
2018-04-23 19:10       ` Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 08/22] rcu: Move __rcu_read_lock() and __rcu_read_unlock() to tree_plugin.h Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 09/22] rcu: Update rcu_bind_gp_kthread() header comment Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 10/22] rcu: Declare rcu_eqs_special_set() in public header Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 11/22] srcu: Add cleanup_srcu_struct_quiesced() Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 12/22] nvme: Avoid flush dependency in delete controller flow Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 13/22] rcu: Exclude near-simultaneous RCU CPU stall warnings Paul E. McKenney
2018-05-03 18:22   ` Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 14/22] rcu: Add leaf-node macros Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 15/22] doc: Ensure whatisRCU.txt actually says what RCU is Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 16/22] EXP: rcu: Add debugging info to assertion Paul E. McKenney
2018-05-03 18:23   ` Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 17/22] EXP: rcu: Abstract addition of debugging information " Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 18/22] EXP: rcu: Add ->boost_tasks " Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 19/22] EXP: rcu: Add debugging info to other assertion Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 20/22] EXP rcu: Add ->qsmask to assertion Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 21/22] EXP rcu: Add checks for setting ->gp_flags Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 22/22] rcu: Use the proper lockdep annotation in dump_blkd_tasks() Paul E. McKenney

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