From: "Paul E. McKenney" <paulmck@kernel.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, rostedt@goodmis.org,
Uladzislau Rezki <urezki@gmail.com>
Subject: Re: [PATCH rcu 13/14] workqueue: Make queue_rcu_work() use call_rcu_flush()
Date: Sun, 23 Oct 2022 20:15:40 -0700 [thread overview]
Message-ID: <20221024031540.GU5600@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <CAEXW_YQgSwMYisZVctXkjFu6_5YhFCpL_E5o5H4oJooS5Syp+g@mail.gmail.com>
On Sun, Oct 23, 2022 at 08:36:00PM -0400, Joel Fernandes wrote:
> Hello,
>
> On Wed, Oct 19, 2022 at 6:51 PM Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > From: Uladzislau Rezki <urezki@gmail.com>
> >
> > call_rcu() changes to save power will slow down RCU workqueue items
> > queued via queue_rcu_work(). This may not be an issue, however we cannot
> > assume that workqueue users are OK with long delays. Use
> > call_rcu_flush() API instead which reverts to the old behavio
>
> On ChromeOS, I can see that queue_rcu_work() is pretty noisy and the
> batching is much better if we can just keep it as call_rcu() instead
> of call_rcu_flush().
>
> Is there really any reason to keep it as call_rcu_flush() ? If I
> recall, the real reason Vlad's system was slowing down was because of
> scsi and the queue_rcu_work() conversion was really a red herring.
There are less than 20 invocations of queue_rcu_work(), so it should
be possible look through each. The low-risk approach is of course to
have queue_rcu_work() use call_rcu_flush().
The next approach might be to have a Kconfig option and/or kernel
boot parameter that allowed a per-system choice.
But it would not hurt to double-check on Android.
Thanx, Paul
> Vlad, any thoughts?
>
> thanks,
>
> - Joel
>
> .
> >
> > Signed-off-by: Uladzislau Rezki <urezki@gmail.com>
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > ---
> > kernel/workqueue.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> > index 7cd5f5e7e0a1b..b4b0e828b529e 100644
> > --- a/kernel/workqueue.c
> > +++ b/kernel/workqueue.c
> > @@ -1771,7 +1771,7 @@ bool queue_rcu_work(struct workqueue_struct *wq, struct rcu_work *rwork)
> >
> > if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
> > rwork->wq = wq;
> > - call_rcu(&rwork->rcu, rcu_work_rcufn);
> > + call_rcu_flush(&rwork->rcu, rcu_work_rcufn);
> > return true;
> > }
> >
> > --
> > 2.31.1.189.g2e36527f23
> >
next prev parent reply other threads:[~2022-10-24 3:19 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-19 22:51 [PATCH rcu 0/14] Lazy call_rcu() updates for v6.2 Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 01/14] rcu: Simplify rcu_init_nohz() cpumask handling Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 02/14] rcu: Fix late wakeup when flush of bypass cblist happens Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 03/14] rcu: Fix missing nocb gp wake on rcu_barrier() Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 04/14] rcu: Make call_rcu() lazy to save power Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 05/14] rcu: Refactor code a bit in rcu_nocb_do_flush_bypass() Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 06/14] rcu: Shrinker for lazy rcu Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 07/14] rcuscale: Add laziness and kfree tests Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 08/14] percpu-refcount: Use call_rcu_flush() for atomic switch Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 09/14] rcu/sync: Use call_rcu_flush() instead of call_rcu Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 10/14] rcu/rcuscale: Use call_rcu_flush() for async reader test Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 11/14] rcu/rcutorture: Use call_rcu_flush() where needed Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 12/14] scsi/scsi_error: Use call_rcu_flush() instead of call_rcu() Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 13/14] workqueue: Make queue_rcu_work() use call_rcu_flush() Paul E. McKenney
2022-10-24 0:36 ` Joel Fernandes
2022-10-24 3:15 ` Paul E. McKenney [this message]
2022-10-24 10:49 ` Uladzislau Rezki
2022-10-24 12:23 ` Uladzislau Rezki
2022-10-24 14:31 ` Joel Fernandes
2022-10-24 15:39 ` Paul E. McKenney
2022-10-24 16:25 ` Uladzislau Rezki
2022-10-24 16:48 ` Paul E. McKenney
2022-10-24 16:55 ` Uladzislau Rezki
2022-10-24 17:08 ` Uladzislau Rezki
2022-10-24 17:20 ` Joel Fernandes
2022-10-24 17:35 ` Paul E. McKenney
2022-10-24 20:12 ` Joel Fernandes
2022-10-24 20:16 ` Joel Fernandes
2022-10-25 10:48 ` Uladzislau Rezki
2022-10-25 15:05 ` Joel Fernandes
2022-10-26 20:35 ` Uladzislau Rezki
2022-10-24 20:19 ` Paul E. McKenney
2022-10-24 20:26 ` Joel Fernandes
2022-10-24 17:40 ` Uladzislau Rezki
2022-10-24 20:08 ` Joel Fernandes
2022-10-25 10:47 ` Uladzislau Rezki
2022-10-28 21:23 ` Joel Fernandes
2022-10-28 21:42 ` Joel Fernandes
2022-10-31 13:21 ` Uladzislau Rezki
2022-10-31 13:37 ` Joel Fernandes
2022-10-31 18:15 ` Joel Fernandes
2022-11-01 4:49 ` Uladzislau Rezki
2022-10-24 16:54 ` Joel Fernandes
2022-10-19 22:51 ` [PATCH rcu 14/14] rxrpc: Use call_rcu_flush() instead of call_rcu() Paul E. McKenney
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