From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Hao Jia <jiahao.os@bytedance.com>, Peter Zijlstra <peterz@infradead.org>
Cc: mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, rostedt@goodmis.org,
bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
linux-kernel@vger.kernel.org
Subject: Re: [External] Re: [PATCH] sched/core: Avoid obvious double update_rq_clock warning
Date: Wed, 20 Apr 2022 21:11:58 +0200 [thread overview]
Message-ID: <df0c4d87-68be-7aef-597f-043b3c7fea59@arm.com> (raw)
In-Reply-To: <c1e7fc17-b091-1da1-7fa8-0490cc7f7e4b@bytedance.com>
On 20/04/2022 10:29, Hao Jia wrote:
> On 4/19/22 6:48 PM, Peter Zijlstra wrote:
>> On Mon, Apr 18, 2022 at 05:09:29PM +0800, Hao Jia wrote:
[...]
>> I'm really not sure about this part though. This is a bit of a mess. The
>> balancer doesn't really need the pinning stuff. I realize you did that
>> because we got the clock annotation mixed up with that, but urgh.
>>
>> Basically we want double_rq_lock() / double_lock_balance() to clear
>> RQCF_UPDATED, right? Perhaps do that directly?
>>
>> (maybe with an inline helper and a wee comment?)
>>
>> The only immediate problem with this would appear to be that
>> _double_rq_lock() behaves differently when it returns 0. Not sure that
>> matters.
>>
>> Hmm?
>
> Thanks for your review comments.
> As you have prompted, the WARN_DOUBLE_CLOCK warning is still triggered
> when _double_rq_lock() returns 0.
> Please review the solution below, and based on your review, I will
> submit the v2 patch as soon as possible.
> Thanks.
[...]
Maybe something like this:
-->8--
From: Dietmar Eggemann <dietmar.eggemann@arm.com>
Date: Wed, 20 Apr 2022 11:12:10 +0200
Subject: [PATCH] sched/core: Clear RQCF_UPDATED in _double_lock_balance() &
double_rq_lock()
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---
kernel/sched/core.c | 6 +++---
kernel/sched/sched.h | 20 ++++++++++++++++----
2 files changed, 19 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 068c088e9584..f4cfe7eea861 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -610,10 +610,10 @@ void double_rq_lock(struct rq *rq1, struct rq *rq2)
swap(rq1, rq2);
raw_spin_rq_lock(rq1);
- if (__rq_lockp(rq1) == __rq_lockp(rq2))
- return;
+ if (__rq_lockp(rq1) != __rq_lockp(rq2))
+ raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);
- raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);
+ rq_clock_clear_update(rq1, rq2);
}
#endif
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 58263f90c559..3a77b10d7cc4 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2515,6 +2515,16 @@ static inline bool rq_order_less(struct rq *rq1, struct rq *rq2)
extern void double_rq_lock(struct rq *rq1, struct rq *rq2);
+#ifdef CONFIG_SCHED_DEBUG
+static inline void rq_clock_clear_update(struct rq *rq1, struct rq *rq2)
+{
+ rq1->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
+ rq2->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
+}
+#else
+static inline void rq_clock_clear_update(struct rq *rq1, struct rq *rq2) {}
+#endif
+
#ifdef CONFIG_PREEMPTION
/*
@@ -2549,14 +2559,15 @@ static inline int _double_lock_balance(struct rq *this_rq, struct rq *busiest)
__acquires(busiest->lock)
__acquires(this_rq->lock)
{
- if (__rq_lockp(this_rq) == __rq_lockp(busiest))
- return 0;
-
- if (likely(raw_spin_rq_trylock(busiest)))
+ if (__rq_lockp(this_rq) == __rq_lockp(busiest) ||
+ likely(raw_spin_rq_trylock(busiest))) {
+ rq_clock_clear_update(this_rq, busiest);
return 0;
+ }
if (rq_order_less(this_rq, busiest)) {
raw_spin_rq_lock_nested(busiest, SINGLE_DEPTH_NESTING);
+ rq_clock_clear_update(this_rq, busiest);
return 0;
}
@@ -2650,6 +2661,7 @@ static inline void double_rq_lock(struct rq *rq1, struct rq *rq2)
BUG_ON(rq1 != rq2);
raw_spin_rq_lock(rq1);
__acquire(rq2->lock); /* Fake it out ;) */
+ rq_clock_clear_update(rq1, rq2);
}
/*
--
2.25.1
next prev parent reply other threads:[~2022-04-20 19:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-18 9:09 [PATCH] sched/core: Avoid obvious double update_rq_clock warning Hao Jia
2022-04-19 10:48 ` Peter Zijlstra
2022-04-20 8:29 ` [External] " Hao Jia
2022-04-20 19:11 ` Dietmar Eggemann [this message]
2022-04-21 7:24 ` Hao Jia
2022-04-21 10:32 ` Dietmar Eggemann
2022-04-21 12:30 ` Dietmar Eggemann
2022-04-21 13:15 ` [External] " Hao Jia
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