linux-kernel - Re: [External] Re: [PATCH] sched/core: Avoid obvious double update_rq

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Date:   Thu, 21 Apr 2022 12:32:17 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Hao Jia <jiahao.os@...edance.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] sched/core: Avoid obvious double
 update_rq_clock warning

On 21/04/2022 09:24, Hao Jia wrote:
> On 2022/4/21 Dietmar Eggemann wrote:
>> 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:

[...]

> Thanks for your review.
> This is very helpful to me.
> If CONFIG_SMP is not enabled, should we just clear the RQCF_UPDATED of
> one of rq1 and q2?
> 
> like this:
> rq1->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);

[...]

We could take care of that within rq_clock_clear_update() if really
needed?
Anyway, for !CONFIG_SMP builds rq_clock_clear_update() has to be defined
outside #ifdef CONFIG_SMP.

-->8--

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3a77b10d7cc4..614b822c667c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2484,6 +2484,17 @@ unsigned long arch_scale_freq_capacity(int cpu)
 }
 #endif
 
+#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);
+#ifdef CONFIG_SMP
+	rq2->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
+#endif
+}
+#else
+static inline void rq_clock_clear_update(struct rq *rq1, struct rq *rq2) {}
+#endif
 
 #ifdef CONFIG_SMP
 
@@ -2515,16 +2526,6 @@ 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
 
 /*