From: Peter Zijlstra <peterz@infradead.org>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Chengming Zhou <zhouchengming@bytedance.com>,
mingo@redhat.com, vincent.guittot@linaro.org, bristot@redhat.com,
zhaolei@cn.fujitsu.com, tj@kernel.org, lizefan.x@bytedance.com,
hannes@cmpxchg.org, linux-kernel@vger.kernel.org,
Paul McKenney <paulmck@kernel.org>
Subject: Re: [PATCH v3 2/3] sched/cpuacct: optimize away RCU read lock
Date: Wed, 9 Mar 2022 00:32:25 +0100 [thread overview]
Message-ID: <YifniVyoJ9NNU+pv@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <f4bc652b-115f-35b5-91db-bad3b30fed9b@samsung.com>
On Wed, Mar 09, 2022 at 12:20:33AM +0100, Marek Szyprowski wrote:
> On 20.02.2022 06:14, Chengming Zhou wrote:
> > Since cpuacct_charge() is called from the scheduler update_curr(),
> > we must already have rq lock held, then the RCU read lock can
> > be optimized away.
> >
> > And do the same thing in it's wrapper cgroup_account_cputime(),
> > but we can't use lockdep_assert_rq_held() there, which defined
> > in kernel/sched/sched.h.
> >
> > Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
>
> This patch landed recently in linux-next as commit dc6e0818bc9a
> ("sched/cpuacct: Optimize away RCU read lock"). On my test systems I
> found that it triggers a following warning in the early boot stage:
>
> Calibrating delay loop (skipped), value calculated using timer
> frequency.. 48.00 BogoMIPS (lpj=240000)
> pid_max: default: 32768 minimum: 301
> Mount-cache hash table entries: 2048 (order: 1, 8192 bytes, linear)
> Mountpoint-cache hash table entries: 2048 (order: 1, 8192 bytes, linear)
> CPU: Testing write buffer coherency: ok
> CPU0: Spectre v2: using BPIALL workaround
>
> =============================
> WARNING: suspicious RCU usage
> 5.17.0-rc5-00050-gdc6e0818bc9a #11458 Not tainted
> -----------------------------
> ./include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage!
Arguably, with the flavours folded again, rcu_dereference_check() ought
to default include rcu_read_lock_sched_held() or its equivalent I
suppose.
Paul?
next prev parent reply other threads:[~2022-03-09 1:19 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-20 5:14 [PATCH v3 1/3] sched/cpuacct: fix charge percpu cpuusage Chengming Zhou
2022-02-20 5:14 ` [PATCH v3 2/3] sched/cpuacct: optimize away RCU read lock Chengming Zhou
2022-03-01 15:24 ` [tip: sched/core] sched/cpuacct: Optimize " tip-bot2 for Chengming Zhou
[not found] ` <CGME20220308232034eucas1p2b0f39cee0f462af6004ebdfbe5bacb9f@eucas1p2.samsung.com>
2022-03-08 23:20 ` [PATCH v3 2/3] sched/cpuacct: optimize " Marek Szyprowski
2022-03-08 23:32 ` Peter Zijlstra [this message]
2022-03-08 23:44 ` Paul E. McKenney
2022-03-09 0:21 ` Paul E. McKenney
2022-03-10 8:45 ` Peter Zijlstra
2022-03-10 15:01 ` Paul E. McKenney
2022-03-12 12:15 ` Peter Zijlstra
2022-03-12 17:44 ` Paul E. McKenney
2022-03-09 3:08 ` [External] " Chengming Zhou
2022-02-20 5:14 ` [PATCH v3 3/3] sched/cpuacct: remove redundant " Chengming Zhou
2022-03-01 15:24 ` [tip: sched/core] sched/cpuacct: Remove " tip-bot2 for Chengming Zhou
[not found] ` <CGME20220308233107eucas1p119a2f5a8d4f5b5eec38ea8dde92b3368@eucas1p1.samsung.com>
2022-03-08 23:31 ` [PATCH v3 3/3] sched/cpuacct: remove " Marek Szyprowski
2022-02-22 18:01 ` [PATCH v3 1/3] sched/cpuacct: fix charge percpu cpuusage Tejun Heo
2022-02-23 9:11 ` Peter Zijlstra
2022-03-01 15:24 ` [tip: sched/core] sched/cpuacct: Fix " tip-bot2 for Chengming Zhou
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