From: "Zhang, Qiang1" <qiang1.zhang@intel.com>
To: Uladzislau Rezki <urezki@gmail.com>,
"Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
RCU <rcu@vger.kernel.org>,
"quic_neeraju@quicinc.com" <quic_neeraju@quicinc.com>,
Boqun Feng <boqun.feng@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
LKML <linux-kernel@vger.kernel.org>,
Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>,
Steven Rostedt <rostedt@goodmis.org>,
Frederic Weisbecker <frederic@kernel.org>
Subject: RE: [PATCH 1/1] Reduce synchronize_rcu() waiting time
Date: Mon, 27 Mar 2023 11:21:23 +0000 [thread overview]
Message-ID: <PH0PR11MB58805561777B77DC69E87711DA8B9@PH0PR11MB5880.namprd11.prod.outlook.com> (raw)
In-Reply-To: <ZBnKKZsSpI8aAk9W@pc636>
> > From: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > Sent: Tuesday, March 21, 2023 6:28 PM
> > [...]
> > Subject: [PATCH 1/1] Reduce synchronize_rcu() waiting time
> >
> > A call to a synchronize_rcu() can be expensive from time point of view.
> > Different workloads can be affected by this especially the ones which use this
> > API in its time critical sections.
> >
>
> This is interesting and meaningful research. ;-)
>
> > For example in case of NOCB scenario the wakeme_after_rcu() callback
> > invocation depends on where in a nocb-list it is located. Below is an example
> > when it was the last out of ~3600 callbacks:
>
Can it be implemented separately as follows? it seems that the code is simpler
(only personal opinion) 😊.
But I didn't test whether this reduce synchronize_rcu() waiting time
+static void rcu_poll_wait_gp(struct rcu_tasks *rtp)
+{
+ unsigned long gp_snap;
+
+ gp_snap = start_poll_synchronize_rcu();
+ while (!poll_state_synchronize_rcu(gp_snap))
+ schedule_timeout_idle(1);
+}
+
+void call_rcu_poll(struct rcu_head *rhp, rcu_callback_t func);
+DEFINE_RCU_TASKS(rcu_poll, rcu_poll_wait_gp, call_rcu_poll,
+ "RCU Poll");
+void call_rcu_poll(struct rcu_head *rhp, rcu_callback_t func)
+{
+ call_rcu_tasks_generic(rhp, func, &rcu_poll);
+}
+EXPORT_SYMBOL_GPL(call_rcu_poll);
+
+void synchronize_rcu_poll(void)
+{
+ synchronize_rcu_tasks_generic(&rcu_poll);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_poll);
+
+static int __init rcu_spawn_poll_kthread(void)
+{
+ cblist_init_generic(&rcu_poll);
+ rcu_poll.gp_sleep = HZ / 10;
+ rcu_spawn_tasks_kthread_generic(&rcu_poll);
+ return 0;
+}
Thanks
Zqiang
> >
> > <snip>
> > <...>-29 [001] d..1. 21950.145313: rcu_batch_start: rcu_preempt
> > CBs=3613 bl=28
> > ...
> > <...>-29 [001] ..... 21950.152578: rcu_invoke_callback: rcu_preempt
> > rhp=00000000b2d6dee8 func=__free_vm_area_struct.cfi_jt
> > <...>-29 [001] ..... 21950.152579: rcu_invoke_callback: rcu_preempt
> > rhp=00000000a446f607 func=__free_vm_area_struct.cfi_jt
> > <...>-29 [001] ..... 21950.152580: rcu_invoke_callback: rcu_preempt
> > rhp=00000000a5cab03b func=__free_vm_area_struct.cfi_jt
> > <...>-29 [001] ..... 21950.152581: rcu_invoke_callback: rcu_preempt
> > rhp=0000000013b7e5ee func=__free_vm_area_struct.cfi_jt
> > <...>-29 [001] ..... 21950.152582: rcu_invoke_callback: rcu_preempt
> > rhp=000000000a8ca6f9 func=__free_vm_area_struct.cfi_jt
> > <...>-29 [001] ..... 21950.152583: rcu_invoke_callback: rcu_preempt
> > rhp=000000008f162ca8 func=wakeme_after_rcu.cfi_jt
> > <...>-29 [001] d..1. 21950.152625: rcu_batch_end: rcu_preempt CBs-
> > invoked=3612 idle=....
> > <snip>
> >
>
> Did the results above tell us that CBs-invoked=3612 during the time 21950.145313 ~ 21950.152625?
>
>Yes.
>
>
> If possible, may I know the steps, commands, and related parameters to produce the results above?
> Thank you!
>
>Build the kernel with CONFIG_RCU_TRACE configuration. Update your "set_event"
>file with appropriate traces:
>
><snip>
>XQ-DQ54:/sys/kernel/tracing # echo rcu:rcu_batch_start rcu:rcu_batch_end rcu:rcu_invoke_callback > set_event
>
>XQ-DQ54:/sys/kernel/tracing # cat set_event
>rcu:rcu_batch_start
>rcu:rcu_invoke_callback
>rcu:rcu_batch_end
>XQ-DQ54:/sys/kernel/tracing #
><snip>
>
>Collect traces as much as you want: XQ-DQ54:/sys/kernel/tracing # echo 1 > tracing_on; sleep 10; echo 0 > tracing_on
>Next problem is how to parse it. Of course you will not be able to parse
>megabytes of traces. For that purpose i use a special C trace parser.
>If you need an example please let me know i can show here.
>
>--
>Uladzislau Rezki
next prev parent reply other threads:[~2023-03-27 11:21 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-21 10:27 [PATCH 1/1] Reduce synchronize_rcu() waiting time Uladzislau Rezki (Sony)
2023-03-21 14:03 ` Zhuo, Qiuxu
2023-03-21 15:15 ` Uladzislau Rezki
2023-03-22 1:49 ` Zhuo, Qiuxu
2023-03-22 6:50 ` Uladzislau Rezki
2023-03-22 11:21 ` Zhuo, Qiuxu
2023-03-27 11:21 ` Zhang, Qiang1 [this message]
2023-03-27 17:47 ` Uladzislau Rezki
2023-03-28 0:14 ` Zhang, Qiang1
2023-03-27 21:23 ` Joel Fernandes
2023-03-28 0:12 ` Zhang, Qiang1
2023-03-28 1:06 ` Paul E. McKenney
2023-03-28 1:32 ` Zhang, Qiang1
2023-03-28 1:59 ` Paul E. McKenney
2023-03-28 2:29 ` Joel Fernandes
2023-03-28 15:26 ` Paul E. McKenney
2023-03-28 22:14 ` Paul E. McKenney
2023-03-30 15:11 ` Joel Fernandes
2023-03-30 19:01 ` Paul E. McKenney
2023-03-30 15:09 ` Joel Fernandes
2023-03-30 15:43 ` Uladzislau Rezki
2023-03-30 18:58 ` Paul E. McKenney
2023-03-30 19:18 ` Uladzislau Rezki
2023-03-30 21:16 ` Paul E. McKenney
2023-03-31 10:55 ` Uladzislau Rezki
2023-03-31 18:39 ` Paul E. McKenney
2023-03-30 18:57 ` Paul E. McKenney
2023-03-27 21:48 ` Steven Rostedt
2023-03-27 21:50 ` Steven Rostedt
2023-03-28 1:28 ` Zhuo, Qiuxu
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