From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Joel Fernandes <joel@joelfernandes.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
Rushikesh S Kadam <rushikesh.s.kadam@intel.com>,
"Uladzislau Rezki (Sony)" <urezki@gmail.com>,
Neeraj upadhyay <neeraj.iitr10@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>, rcu <rcu@vger.kernel.org>,
Vineeth Pillai <vineeth@bitbyteword.org>
Subject: Re: [PATCH v4 00/14] Implement call_rcu_lazy() and miscellaneous fixes
Date: Wed, 31 Aug 2022 17:26:58 +0200 [thread overview]
Message-ID: <20220831152658.GA89704@lothringen> (raw)
In-Reply-To: <20220830164634.GC6159@paulmck-ThinkPad-P17-Gen-1>
On Tue, Aug 30, 2022 at 09:46:34AM -0700, Paul E. McKenney wrote:
> > Although who knows, may be some periodic file operation while idle are specific
> > to Android. I'll try to trace lazy callbacks while idle and the number of grace
> > periods associated.
>
> Sounds like a good start.
>
> And yes, we don't need to show that the whole !NOCB world needs this,
> just some significant portion of it. But we do need some decent evidence.
> After all, it is all too easy to do a whole lot of work and find that
> the expected benefits fail to materialize.
So here is some quick test. I made a patch that replaces Joel's 1st patch
with an implementation of call_rcu_lazy() that queues lazy callbacks
through the regular call_rcu() way but it counts them in a lazy_count.
Upon idle entry it reports whether the tick is retained solely by lazy
callbacks or not.
I get periodic and frequent results on my idle test box, something must be
opening/closing some file periodically perhaps.
Anyway the thing can be tested with this branch:
git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
rcu/lazy-trace
Excerpt:
<idle>-0 [007] d..1. 414.226966: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 414.228271: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 414.232269: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 414.236269: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 414.468048: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 414.468268: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 414.472268: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 414.476269: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 419.500577: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 419.504253: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 419.508250: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 419.512249: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 419.566881: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 419.568252: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 419.572249: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 419.576255: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 424.666873: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 424.668233: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 424.672230: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 424.676232: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 424.737283: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 424.740233: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 424.744230: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 424.748231: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 429.767922: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 429.768209: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 429.772212: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 429.776212: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 429.972931: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 429.976214: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 429.980211: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [007] d..1. 429.984212: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [003] d..1. 430.402139: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [003] d..1. 430.404211: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [003] d..1. 430.404290: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [003] d..1. 430.408235: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [003] d..1. 430.408304: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
<idle>-0 [003] d..1. 430.412215: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle
Thanks.
next prev parent reply other threads:[~2022-08-31 15:27 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-19 20:48 [PATCH v4 00/14] Implement call_rcu_lazy() and miscellaneous fixes Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 01/14] rcu: Introduce call_rcu_lazy() API implementation Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 02/14] rcu: shrinker for lazy rcu Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 03/14] rcuscale: Add laziness and kfree tests Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 04/14] fs: Move call_rcu() to call_rcu_lazy() in some paths Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 05/14] rcutorture: Add test code for call_rcu_lazy() Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 06/14] debug: Toggle lazy at runtime and change flush jiffies Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 07/14] cred: Move call_rcu() to call_rcu_lazy() Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 08/14] security: " Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 09/14] net/core: " Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 10/14] kernel: Move various core kernel usages " Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 11/14] lib: Move call_rcu() " Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 12/14] i915: " Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 13/14] fork: Move thread_stack_free_rcu to call_rcu_lazy Joel Fernandes (Google)
2022-08-19 20:48 ` [PATCH v4 14/14] rcu/tree: Move trace_rcu_callback() before bypassing Joel Fernandes (Google)
2022-08-29 13:40 ` [PATCH v4 00/14] Implement call_rcu_lazy() and miscellaneous fixes Frederic Weisbecker
2022-08-29 16:45 ` Joel Fernandes
2022-08-29 19:46 ` Frederic Weisbecker
2022-08-29 20:31 ` Paul E. McKenney
2022-08-29 20:54 ` Joel Fernandes
2022-08-30 10:50 ` Frederic Weisbecker
2022-08-30 11:47 ` Paul E. McKenney
2022-08-29 20:36 ` Joel Fernandes
2022-08-29 20:42 ` Paul E. McKenney
2022-08-29 20:48 ` Joel Fernandes
2022-08-30 10:57 ` Frederic Weisbecker
2022-08-30 10:53 ` Frederic Weisbecker
2022-08-30 11:43 ` Paul E. McKenney
2022-08-30 16:03 ` Frederic Weisbecker
2022-08-30 16:22 ` Frederic Weisbecker
2022-08-30 16:44 ` Uladzislau Rezki
2022-08-30 18:53 ` Joel Fernandes
2022-09-01 11:29 ` Frederic Weisbecker
2022-09-01 11:59 ` Uladzislau Rezki
2022-09-01 14:41 ` Paul E. McKenney
2022-09-01 15:30 ` Frederic Weisbecker
2022-09-01 16:11 ` Joel Fernandes
2022-09-01 16:52 ` Paul E. McKenney
2022-09-01 15:13 ` Frederic Weisbecker
2022-09-01 16:07 ` Joel Fernandes
2022-08-30 16:46 ` Paul E. McKenney
2022-08-31 15:26 ` Frederic Weisbecker [this message]
2022-09-01 14:39 ` Paul E. McKenney
2022-09-01 14:58 ` Frederic Weisbecker
2022-09-01 16:07 ` Joel Fernandes
2022-09-01 16:49 ` Paul E. McKenney
2022-09-01 18:28 ` Frederic Weisbecker
2022-09-01 20:36 ` Paul E. McKenney
2022-08-30 18:46 ` Joel Fernandes
2022-08-30 10:26 ` Frederic Weisbecker
2022-08-30 18:40 ` Joel Fernandes
2022-08-29 19:57 ` Paul E. McKenney
2022-08-30 10:43 ` Frederic Weisbecker
2022-08-30 12:08 ` Paul E. McKenney
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