From: Qais Yousef <qais.yousef@arm.com>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Doug Anderson <dianders@chromium.org>,
Jonathan Corbet <corbet@lwn.net>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Luis Chamberlain <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>,
Iurii Zaikin <yzaikin@google.com>,
Quentin Perret <qperret@google.com>,
Patrick Bellasi <patrick.bellasi@matbug.net>,
Pavan Kondeti <pkondeti@codeaurora.org>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v6 1/2] sched/uclamp: Add a new sysctl to control RT default boost value
Date: Wed, 8 Jul 2020 14:08:33 +0100 [thread overview]
Message-ID: <20200708130831.4oaukv65hbano3j7@e107158-lin> (raw)
In-Reply-To: <jhjwo3e6zd1.mognet@arm.com>
On 07/08/20 12:05, Valentin Schneider wrote:
> > AFAIU rcu_read_lock() is light weight. So having the protection applied is more
> > robust against future changes.
>
> So I think the one thing you win by having this dance with mb's and the
> suggested handling of the task list is that you do not need any
> rcu_synchronize() anymore. Both approaches have merit, it's just that the
> way I understood the suggestion to add sched_post_fork() was to simplify
> the ordering of the update with the aforementioned scheme.
The synchronize_rcu() is not for sched_post_fork(). It is to deal with the
preemption problem.
>
> >
> >>
> >> sched_post_fork() being preempted out is a bit more annoying, but what
> >> prevents us from making that bit preempt-disabled?
> >
> > preempt_disable() is not friendly to RT and heavy handed approach IMO.
> >
>
> True, but this is both an infrequent and slow sysctl path, so I don't think
> RT would care much.
There's an easy answer for that. But first I'm not sure what problem are we
discussing here.
What is the problem with rcu? And how is preempt_disable() fixes it or improves
on it?
Thanks
--
Qais Yousef
next prev parent reply other threads:[~2020-07-08 13:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-06 14:28 [PATCH v6 0/2] sched/uclamp: new sysctl for default RT boost value Qais Yousef
2020-07-06 14:28 ` [PATCH v6 1/2] sched/uclamp: Add a new sysctl to control RT default " Qais Yousef
2020-07-06 15:49 ` Valentin Schneider
2020-07-07 9:34 ` Qais Yousef
2020-07-07 11:30 ` Valentin Schneider
2020-07-07 12:36 ` Qais Yousef
2020-07-08 11:05 ` Valentin Schneider
2020-07-08 13:08 ` Qais Yousef [this message]
2020-07-08 21:45 ` Valentin Schneider
2020-07-07 11:39 ` Valentin Schneider
2020-07-07 12:58 ` Qais Yousef
2020-07-13 11:21 ` Peter Zijlstra
2020-07-13 11:36 ` peterz
2020-07-13 12:12 ` Qais Yousef
2020-07-13 13:35 ` Peter Zijlstra
2020-07-13 14:27 ` Qais Yousef
2020-07-13 16:54 ` Peter Zijlstra
2020-07-13 18:09 ` Qais Yousef
2020-07-06 14:28 ` [PATCH v6 2/2] Documentation/sysctl: Document uclamp sysctl knobs Qais Yousef
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