From: Uladzislau Rezki <urezki@gmail.com>
To: "Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
"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: Tue, 21 Mar 2023 16:15:53 +0100 [thread overview]
Message-ID: <ZBnKKZsSpI8aAk9W@pc636> (raw)
In-Reply-To: <IA1PR11MB617169A10E6DDE3C1168605D89819@IA1PR11MB6171.namprd11.prod.outlook.com>
On Tue, Mar 21, 2023 at 02:03:19PM +0000, Zhuo, Qiuxu wrote:
> > 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:
> >
> > <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:[~2023-03-21 15:16 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 [this message]
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
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
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=ZBnKKZsSpI8aAk9W@pc636 \
--to=urezki@gmail.com \
--cc=boqun.feng@gmail.com \
--cc=frederic@kernel.org \
--cc=joel@joelfernandes.org \
--cc=linux-kernel@vger.kernel.org \
--cc=oleksiy.avramchenko@sony.com \
--cc=paulmck@kernel.org \
--cc=qiuxu.zhuo@intel.com \
--cc=quic_neeraju@quicinc.com \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
/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;
as well as URLs for NNTP newsgroup(s).