From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: 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, rostedt@goodmis.org,
dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com,
oleg@redhat.com, joel@joelfernandes.org
Subject: Re: [PATCH tip/core/rcu 16/27] rcu: Add comment documenting how rcu_seq_snap works
Date: Tue, 26 Jun 2018 12:31:46 -0700 [thread overview]
Message-ID: <20180626193146.GK3593@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180626192113.GM2494@hirez.programming.kicks-ass.net>
On Tue, Jun 26, 2018 at 09:21:13PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 26, 2018 at 11:08:55AM -0700, Paul E. McKenney wrote:
> > On Tue, Jun 26, 2018 at 07:14:54PM +0200, Peter Zijlstra wrote:
> > > On Mon, Jun 25, 2018 at 05:35:02PM -0700, Paul E. McKenney wrote:
> > > > From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
> > > >
> > > > rcu_seq_snap may be tricky to decipher. Lets document how it works with
> > > > an example to make it easier.
> > >
> > > Since you had me looking at them functions; why isn't rcu_seq_snap()
> > > using smp_load_acquire() and rcu_seq_end() using smp_store_release() ?
> > > Their respective comments seem to suggest that would be sufficent.
> >
> > I do not believe that this would suffice. Would it make sense to refer
> > to Documentation/RCU/Design/Memory-Ordering in the comment header?
>
> No, because I can't read that thing in an editor.
>
> > Except that this would invite sprinkling this pathname far and wide...
> >
> > The key point is that these functions are part of the any-to-any
> > memory-ordering guarantee that RCU grace periods provide.
>
> Then the existing comment is misleading and really needs change.
Would it be sufficient to add something like "The memory barrier is
required to support the many-to-many ordering guaranteed by RCU grace
periods"?
Thanx, Paul
next prev parent reply other threads:[~2018-06-26 19:29 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-26 0:34 [PATCH tip/core/rcu 0/27] Post-gp_seq miscellaneous fixes for v4.19 Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 01/27] rcu: Make rcu_read_unlock_special() static Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 02/27] rcu: Improve rcu_note_voluntary_context_switch() reporting Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 03/27] rcu: rcupdate.h: Get rid of Sphinx warnings at rcu_pointer_handoff() Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 04/27] rcu: Use pr_fmt to prefix "rcu: " to logging output Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 05/27] rcu: Improve RCU-tasks naming and comments Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 06/27] rcu: Mark task as .need_qs less aggressively Paul E. McKenney
2018-06-26 17:08 ` Peter Zijlstra
2018-06-26 18:03 ` Paul E. McKenney
2018-06-26 21:38 ` Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 07/27] rcu: Inline rcu_dynticks_momentary_idle() into its sole caller Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 08/27] rcu: Clarify and correct the rcu_preempt_qs() header comment Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 09/27] rcu: Remove unused rcu_kick_nohz_cpu() function Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 10/27] rcu: Remove unused local variable "cpu" Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 11/27] rcu: Remove "inline" from panic_on_rcu_stall() and rcu_blocking_is_gp() Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 12/27] rcu: Remove "inline" from rcu_torture_print_module_parms() Paul E. McKenney
2018-06-26 0:34 ` [PATCH tip/core/rcu 13/27] rcu: Remove "inline" from rcu_perf_print_module_parms() Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 14/27] rcu: Remove __maybe_unused from rcu_cpu_has_callbacks() Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 15/27] rcu: Use RCU CPU stall timeout for rcu_check_gp_start_stall() Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 16/27] rcu: Add comment documenting how rcu_seq_snap works Paul E. McKenney
2018-06-26 17:14 ` Peter Zijlstra
2018-06-26 18:08 ` Paul E. McKenney
2018-06-26 19:21 ` Peter Zijlstra
2018-06-26 19:31 ` Paul E. McKenney [this message]
2018-06-26 20:15 ` Peter Zijlstra
2018-06-26 22:27 ` Paul E. McKenney
2018-06-26 17:30 ` Peter Zijlstra
2018-06-26 18:10 ` Paul E. McKenney
2018-06-26 19:27 ` Peter Zijlstra
2018-06-27 4:39 ` Joel Fernandes
2018-06-27 17:54 ` Paul E. McKenney
2018-06-27 18:27 ` Joel Fernandes
2018-06-27 19:11 ` Paul E. McKenney
2018-06-28 5:10 ` Joel Fernandes
2018-06-28 17:42 ` Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 17/27] rcu: Speed up calling of RCU tasks callbacks Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 18/27] rcu: Add comment to the last sleep in the rcu tasks loop Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 19/27] rcu: Add diagnostics for rcutorture writer stall warning Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 20/27] rcu: Check the range of jiffies_till_{first,next}_fqs when setting them Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 21/27] doc: Update synchronize_rcu() definition in whatisRCU.txt Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 22/27] rcu: Make rcu_seq_diff() more exact Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 23/27] MAINTAINERS: Update RCU, SRCU, and TORTURE-TEST entries Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 24/27] rcu: Print stall-warning NMI dyntick state in hexadecimal Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 25/27] srcu: Add grace-period number to rcutorture statistics printout Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 26/27] rculist: Improve documentation for list_for_each_entry_from_rcu() Paul E. McKenney
2018-06-26 0:35 ` [PATCH tip/core/rcu 27/27] rcu: Assign higher prio to RCU threads if rcutorture is built-in Paul E. McKenney
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180626193146.GK3593@linux.vnet.ibm.com \
--to=paulmck@linux.vnet.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=dhowells@redhat.com \
--cc=dipankar@in.ibm.com \
--cc=edumazet@google.com \
--cc=fweisbec@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox