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Message-ID: <9b411c72-eda8-e98f-4e03-526ea645a7db@bytedance.com>
Date: Sat, 30 Apr 2022 15:24:26 +0800
From: Hao Jia <jiahao.os@...edance.com>
To: Dietmar Eggemann <dietmar.eggemann@....com>, mingo@...hat.com,
peterz@...radead.org, juri.lelli@...hat.com,
vincent.guittot@...aro.org, rostedt@...dmis.org,
bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com
Cc: linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH v3 1/2] sched/core: Avoid obvious double
update_rq_clock warning
On 2022/4/29 Dietmar Eggemann wrote:
> On 27/04/2022 10:00, Hao Jia wrote:
>
> [...]
>
> LGTM, comments are only nit-picks.
>
>> Since we directly use raw_spin_rq_lock() to acquire rq lock instead of
>> rq_lock(), there is no corresponding change to rq->clock_update_flags.
>> In particular, we have obtained the rq lock of other cores,
>
> s/cores/CPUs, with SMT, a core can have multiple (logical) CPUs.
Thanks for your review comments.
I will do it in patch v4.
Thanks.
>
> [...]
>
>> So we need to clear RQCF_UPDATED of rq->clock_update_flags synchronously
>> to avoid the WARN_DOUBLE_CLOCK warning.
>
> Why you mention `synchronously` here? Isn't this obvious? (1)
I will do it in patch v4.
Thanks.
>
> [...]
>
>> @@ -1833,6 +1833,7 @@ select_task_rq_dl(struct task_struct *p, int cpu, int flags)
>> static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused)
>> {
>> struct rq *rq;
>> + struct rq_flags rf;
>
> - struct rq *rq;
> struct rq_flags rf;
> + struct rq *rq;
>
> Use reverse fir tree order for variable declarations.
> (./Documentation/process/maintainer-tip.rst)
I will do it in patch v4.
Thanks.
>
> [...]
>
>> +#ifdef CONFIG_SCHED_DEBUG
>> +/*
>> + * In double_lock_balance()/double_rq_lock(), we use raw_spin_rq_lock() to acquire
>> + * rq lock instead of rq_lock(). So at the end of these two functions we need to
>> + * call double_rq_clock_clear_update() synchronously to clear RQCF_UPDATED of
> ^^^^^^^^^^^^^
> (1)
>
>> + * rq->clock_update_flags to avoid the WARN_DOUBLE_CLOCK warning.
>> + */
>> +static inline void double_rq_clock_clear_update(struct rq *rq1, struct rq *rq2)
>> +{
>> + rq1->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
>> + /*
>> + * If CONFIG_SMP is not defined, rq1 and rq2 are the same,
>> + * so we just clear RQCF_UPDATED one of them.
>> + */
>
> Maybe shorter:
>
> /* rq1 == rq2 for !CONFIG_SMP, so just clear RQCF_UPDATED once. */
I will do it in patch v4.
Thanks.
>
> [...]
>
>> @@ -2543,14 +2564,15 @@ 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))) {
>
> indention:
>
> if (__rq_lockp(this_rq) == __rq_lockp(busiest) ||
> - likely(raw_spin_rq_trylock(busiest))) {
> + likely(raw_spin_rq_trylock(busiest))) {
Thanks again for your review and suggestion.
I will do it in patch v4.
Thanks.
>
> [...]
>
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
>
> Tested on Arm64 Juno with mainline & preempt-rt (linux-5.17.y-rt).
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