From: Valentin Schneider <vschneid@redhat.com>
To: Frederic Weisbecker <frederic@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>,
Boqun Feng <boqun.feng@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang1211@gmail.com>
Subject: Re: [PATCH v2 18/27] rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_changed_since()
Date: Mon, 13 May 2024 20:40:09 +0200 [thread overview]
Message-ID: <xhsmhttj1h7xy.mognet@vschneid-thinkpadt14sgen2i.remote.csb> (raw)
In-Reply-To: <Zjta9-jCNHmAAh6b@localhost.localdomain>
On 08/05/24 12:59, Frederic Weisbecker wrote:
> Le Tue, May 07, 2024 at 10:14:08AM -0700, Paul E. McKenney a écrit :
>> On Tue, May 07, 2024 at 03:48:18PM +0200, Frederic Weisbecker wrote:
>> > Indeed in practice the function only checks a change. But semantically it really
>> > checks a trip to eqs because this function is only ever called after a failing
>> > call to rcu_dynticks_in_eqs().
>> >
>> > So not sure about that one rename. Paul?
>>
>> As you say, Valentin is technically correct. Me, I am having a hard
>> time getting too excited one way or the other. ;-)
>>
>> I suggest thinking in terms of rate-bounding the change. If you do
>> change it, don't change it again for a few years.
>
> Makes sense!
>
>>
>> Either way, should comments be changed or added?
>>
>> Of course, the scientific way to evaluate this is to whose a couple
>> dozen people the old code and a couple dozen other people the new code,
>> and see if one group or the other has statistically significantly lower
>> levels of confusion. I don't see how this is feasible, but it is the
>> (painfully) correct way. On the other hand, it would have the beneficial
>> side effect of getting more people exposed to Linux-kernel-RCU internals.
>> Unfortunately, it might also have the additional side effect of making
>> them (more) annoyed at RCU. ;-)
>
> Sounds good!
>
> I divided myself in two blank RCU subjects for a double blind study
> and locked those people up overnight with a paper containing both proposals.
>
> I opened the door five minutes ago and they both elected by mutual agreement
> rcu_watching_changed_since()! Also they are thirsty.
>
> Congratulations Valentin! :-)
:-)
Now, not that I like wasting everyone's time, but... I hadn't taken a step
back to realize the calling context implied this would always be used to
check an entry into EQS, per the waiting loop structures. With this in
mind, how about the following?
/**
* rcu_watching_stopped_since() - Has RCU stopped watching a given CPU since
* the specified @snap?
*
* @rdp: The rcu_data corresponding to the CPU for which to check EQS.
* @snap: rcu_watching snapshot taken when the CPU wasn't in an EQS.
*
* Returns true if the CPU corresponding to @rcu_data has spent some time in an
* extended quiescent state since @snap. Note that this doesn't check if it
* /still/ is in an EQS, just that it went through one since @snap.
*
* This is meant to be used in a loop waiting for a CPU to go through an EQS.
*/
static bool rcu_watching_stopped_since(struct rcu_data *rdp, int snap)
{
if (WARN_ON_ONCE(rcu_watching_in_eqs(snap)))
return true;
return snap != rcu_dynticks_snap(rdp->cpu);
}
next prev parent reply other threads:[~2024-05-13 18:40 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-30 9:17 [PATCH v2 00/27] context_tracking, rcu: Spring cleaning renaming Valentin Schneider
2024-04-30 9:17 ` [PATCH v2 01/27] treewide: context_tracking: Rename CONTEXT_* into CT_STATE_* Valentin Schneider
2024-04-30 9:17 ` [PATCH v2 02/27] context_tracking, rcu: Rename RCU_DYNTICKS_IDX into CT_RCU_WATCHING Valentin Schneider
2024-05-06 10:39 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 03/27] context_tracking, rcu: Rename ct_dynticks() into ct_rcu_watching() Valentin Schneider
2024-05-06 10:41 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 04/27] context_tracking, rcu: Rename ct_dynticks_cpu() into ct_rcu_watching_cpu() Valentin Schneider
2024-05-06 10:43 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 05/27] context_tracking, rcu: Rename ct_dynticks_cpu_acquire() into ct_rcu_watching_cpu_acquire() Valentin Schneider
2024-05-06 10:45 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 06/27] context_tracking, rcu: Rename struct context_tracking .dynticks_nesting into .nesting Valentin Schneider
2024-05-06 10:48 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 07/27] context_tracking, rcu: Rename ct_dynticks_nesting() into ct_nesting() Valentin Schneider
2024-05-06 11:01 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 08/27] context_tracking, rcu: Rename ct_dynticks_nesting_cpu() into ct_nesting_cpu() Valentin Schneider
2024-05-06 20:09 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 09/27] context_tracking, rcu: Rename struct context_tracking .dynticks_nmi_nesting into .nmi_nesting Valentin Schneider
2024-05-06 20:19 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 10/27] context_tracking, rcu: Rename ct_dynticks_nmi_nesting() into ct_nmi_nesting() Valentin Schneider
2024-05-06 20:50 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 11/27] context_tracking, rcu: Rename ct_dynticks_nmi_nesting_cpu() into ct_nmi_nesting_cpu() Valentin Schneider
2024-05-06 21:03 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 12/27] context_tracking, rcu: Rename DYNTICK_IRQ_NONIDLE into CT_NESTING_IRQ_NONIDLE Valentin Schneider
2024-05-06 21:06 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 13/27] context_tracking, rcu: Rename rcu_dynticks_task*() into rcu_task*() Valentin Schneider
2024-05-06 21:15 ` Frederic Weisbecker
2024-05-08 14:39 ` Frederic Weisbecker
2024-05-13 18:39 ` Valentin Schneider
2024-04-30 9:17 ` [PATCH v2 14/27] context_tracking, rcu: Rename rcu_dynticks_curr_cpu_in_eqs() into rcu_watching_curr_cpu() Valentin Schneider
2024-05-06 22:00 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 15/27] rcu: Rename rcu_dynticks_eqs_online() into rcu_watching_eqs_online() Valentin Schneider
2024-05-06 22:18 ` Frederic Weisbecker
2024-05-07 8:59 ` Valentin Schneider
2024-04-30 9:17 ` [PATCH v2 16/27] rcu: Rename rcu_dynticks_snap() into rcu_watching_snap() Valentin Schneider
2024-05-07 13:11 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 17/27] rcu: Rename rcu_dynticks_in_eqs() into rcu_watching_in_eqs() Valentin Schneider
2024-05-07 13:32 ` Frederic Weisbecker
2024-05-07 15:48 ` Valentin Schneider
2024-05-08 10:46 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 18/27] rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_changed_since() Valentin Schneider
2024-05-07 13:48 ` Frederic Weisbecker
2024-05-07 17:14 ` Paul E. McKenney
2024-05-08 10:59 ` Frederic Weisbecker
2024-05-13 18:40 ` Valentin Schneider [this message]
2024-05-14 10:42 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 19/27] rcu: Rename rcu_dynticks_zero_in_eqs() into rcu_watching_zero_in_eqs() Valentin Schneider
2024-05-08 12:43 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 20/27] rcu: Rename struct rcu_data .dynticks_snap into .watching_snap Valentin Schneider
2024-05-08 12:55 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 21/27] rcu: Rename struct rcu_data .exp_dynticks_snap into .exp_watching_snap Valentin Schneider
2024-05-08 13:06 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 22/27] rcu: Rename dyntick_save_progress_counter() into eqs_save_progress_counter() Valentin Schneider
2024-05-08 13:21 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 23/27] rcu: Rename rcu_implicit_dynticks_qs() into rcu_implicit_eqs() Valentin Schneider
2024-04-30 9:17 ` [PATCH v2 24/27] rcu: Rename rcu_momentary_dyntick_idle() into rcu_momentary_eqs() Valentin Schneider
2024-05-08 13:30 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 25/27] context_tracking, rcu: Rename stray ->dynticks comments Valentin Schneider
2024-05-08 13:39 ` Frederic Weisbecker
2024-04-30 9:17 ` [PATCH v2 26/27] rcu: Update stray documentation references to rcu_dynticks_eqs_{enter, exit}() Valentin Schneider
2024-05-08 14:55 ` Frederic Weisbecker
2024-05-13 18:40 ` Valentin Schneider
2024-04-30 9:17 ` [PATCH v2 27/27] context_tracking, rcu: Rename rcu_dyntick trace event into rcu_watching Valentin Schneider
2024-05-08 13:59 ` Frederic Weisbecker
2024-05-13 18:40 ` Valentin Schneider
2024-05-14 12:09 ` Frederic Weisbecker
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