From: Peter Zijlstra <peterz@infradead.org>
To: Juri Lelli <juri.lelli@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>, Qais Yousef <qyousef@layalina.io>,
Waiman Long <longman@redhat.com>, Tejun Heo <tj@kernel.org>,
Zefan Li <lizefan.x@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>, Hao Luo <haoluo@google.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it,
claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it,
bristot@redhat.com, mathieu.poirier@linaro.org,
cgroups@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
Wei Wang <wvw@google.com>, Rick Yiu <rickyiu@google.com>,
Quentin Perret <qperret@google.com>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Sudeep Holla <sudeep.holla@arm.com>
Subject: Re: [PATCH v2 2/6] sched/cpuset: Bring back cpuset_mutex
Date: Thu, 4 May 2023 08:18:42 +0200 [thread overview]
Message-ID: <20230504061842.GC1734100@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230503072228.115707-3-juri.lelli@redhat.com>
On Wed, May 03, 2023 at 09:22:24AM +0200, Juri Lelli wrote:
> /*
> - * There are two global locks guarding cpuset structures - cpuset_rwsem and
> + * There are two global locks guarding cpuset structures - cpuset_mutex and
> * callback_lock. We also require taking task_lock() when dereferencing a
> * task's cpuset pointer. See "The task_lock() exception", at the end of this
> - * comment. The cpuset code uses only cpuset_rwsem write lock. Other
> - * kernel subsystems can use cpuset_read_lock()/cpuset_read_unlock() to
> - * prevent change to cpuset structures.
> + * comment. The cpuset code uses only cpuset_mutex. Other kernel subsystems
> + * can use cpuset_lock()/cpuset_unlock() to prevent change to cpuset
> + * structures.
> *
> * A task must hold both locks to modify cpusets. If a task holds
> - * cpuset_rwsem, it blocks others wanting that rwsem, ensuring that it
> - * is the only task able to also acquire callback_lock and be able to
> - * modify cpusets. It can perform various checks on the cpuset structure
> - * first, knowing nothing will change. It can also allocate memory while
> - * just holding cpuset_rwsem. While it is performing these checks, various
> - * callback routines can briefly acquire callback_lock to query cpusets.
> - * Once it is ready to make the changes, it takes callback_lock, blocking
> - * everyone else.
> + * cpuset_mutex, it blocks others, ensuring that it is the only task able to
> + * also acquire callback_lock and be able to modify cpusets. It can perform
> + * various checks on the cpuset structure first, knowing nothing will change.
> + * It can also allocate memory while just holding cpuset_mutex. While it is
> + * performing these checks, various callback routines can briefly acquire
> + * callback_lock to query cpusets. Once it is ready to make the changes, it
> + * takes callback_lock, blocking everyone else.
> *
> * Calls to the kernel memory allocator can not be made while holding
> * callback_lock, as that would risk double tripping on callback_lock
> @@ -403,16 +402,16 @@ static struct cpuset top_cpuset = {
> * guidelines for accessing subsystem state in kernel/cgroup.c
> */
>
> -DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
> +static DEFINE_MUTEX(cpuset_mutex);
Perhaps extend the comment to state you explicitly want a mutex for PI
etc.. ?
next prev parent reply other threads:[~2023-05-04 6:19 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-03 7:22 [PATCH v2 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration Juri Lelli
2023-05-03 7:22 ` [PATCH v2 1/6] cgroup/cpuset: Rename functions dealing with DEADLINE accounting Juri Lelli
2023-05-03 17:54 ` Waiman Long
2023-05-03 7:22 ` [PATCH v2 2/6] sched/cpuset: Bring back cpuset_mutex Juri Lelli
2023-05-03 17:55 ` Waiman Long
2023-05-04 6:18 ` Peter Zijlstra [this message]
2023-05-04 8:13 ` Juri Lelli
2023-05-04 6:21 ` Peter Zijlstra
2023-05-04 8:13 ` Juri Lelli
2023-05-03 7:22 ` [PATCH v2 3/6] sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets Juri Lelli
2023-05-03 17:56 ` Waiman Long
2023-05-03 7:22 ` [PATCH v2 4/6] cgroup/cpuset: Iterate only if DEADLINE tasks are present Juri Lelli
2023-05-03 17:56 ` Waiman Long
2023-05-03 7:22 ` [PATCH v2 5/6] sched/deadline: Create DL BW alloc, free & check overflow interface Juri Lelli
2023-05-03 17:45 ` Waiman Long
2023-05-04 6:23 ` Peter Zijlstra
2023-05-04 8:15 ` Juri Lelli
2023-05-04 17:21 ` Dietmar Eggemann
2023-05-03 7:22 ` [PATCH v2 6/6] cgroup/cpuset: Free DL BW in case can_attach() fails Juri Lelli
2023-05-03 18:02 ` Waiman Long
2023-05-04 6:25 ` [PATCH v2 0/6] sched/deadline: cpuset: Rework DEADLINE bandwidth restoration Peter Zijlstra
2023-05-04 8:17 ` Juri Lelli
2023-05-05 19:31 ` Tejun Heo
2023-05-08 8:02 ` Juri Lelli
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=20230504061842.GC1734100@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=agordeev@linux.ibm.com \
--cc=bristot@redhat.com \
--cc=cgroups@vger.kernel.org \
--cc=claudio@evidence.eu.com \
--cc=dietmar.eggemann@arm.com \
--cc=gor@linux.ibm.com \
--cc=hannes@cmpxchg.org \
--cc=haoluo@google.com \
--cc=hca@linux.ibm.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=lizefan.x@bytedance.com \
--cc=longman@redhat.com \
--cc=luca.abeni@santannapisa.it \
--cc=mathieu.poirier@linaro.org \
--cc=mingo@kernel.org \
--cc=qperret@google.com \
--cc=qyousef@layalina.io \
--cc=rickyiu@google.com \
--cc=rostedt@goodmis.org \
--cc=sudeep.holla@arm.com \
--cc=tj@kernel.org \
--cc=tommaso.cucinotta@santannapisa.it \
--cc=vincent.guittot@linaro.org \
--cc=wvw@google.com \
/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).