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Date:   Wed, 4 Oct 2023 23:35:26 +0800
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Subject: Re: [PATCH v4] sched/rt: move back to RT_GROUP_SCHED and rename it
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To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@kernel.org>, mingo@redhat.com,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
        linux-kernel@vger.kernel.org,
        kernel test robot <oliver.sang@intel.com>
References: <20230803050317.2240948-1-yajun.deng@linux.dev>
 <ZRvkM1lxsTrHb2Ox@gmail.com> <93aa2ee6-3ee4-0129-7160-d3684ba67f56@linux.dev>
 <20231003163719.GG1539@noisy.programming.kicks-ass.net>
From:   Yajun Deng <yajun.deng@linux.dev>
In-Reply-To: <20231003163719.GG1539@noisy.programming.kicks-ass.net>
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On 2023/10/4 00:37, Peter Zijlstra wrote:
> On Tue, Oct 03, 2023 at 10:55:50PM +0800, Yajun Deng wrote:
>
>> @Peter, I think I split up this patch into 2 separate patches:
>>
>>           sched/rt: Introduce for_each_sched_rt_entity_back() & use it
> Why ?? Having that macro makes no sense what so ever. You can't use it,
> unless you set up the back pointers first. It is not a self contained
> piece of functionality.


The 2nd patch rely on this patch. It will be used in dequeue_rt_stack. 
We need to add a macro first,

because the 'back' will be not exist after the 2nd patch when disable 
CONFIG_RT_GROUP_SCHED.

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 88fc98601413..0b6b4a715d6e 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -520,6 +520,9 @@ static inline struct task_group 
*next_task_group(struct task_group *tg)
  #define for_each_sched_rt_entity(rt_se) \
      for (; rt_se; rt_se = rt_se->parent)

+#define for_each_sched_rt_back(rt_se) \
+    for (; rt_se; rt_se = rt_se->back)
+
  static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
  {
      return rt_se->my_q;
@@ -625,6 +628,9 @@ typedef struct rt_rq *rt_rq_iter_t;
  #define for_each_sched_rt_entity(rt_se) \
      for (; rt_se; rt_se = NULL)

+#define for_each_sched_rt_entity_back(rt_se) \
+    for_each_sched_rt_entity(rt_se)
+
  static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
  {
      return NULL;
@@ -1445,7 +1451,8 @@ static void dequeue_rt_stack(struct 
sched_rt_entity *rt_se, unsigned int flags)

      rt_nr_running = rt_rq_of_se(back)->rt_nr_running;

-    for (rt_se = back; rt_se; rt_se = rt_se->back) {
+    rt_se = back;
+    for_each_sched_rt_entity_back(rt_se) {
          if (on_rt_rq(rt_se))
              __dequeue_rt_entity(rt_se, flags);
      }


>
>>          sched/rt: Move sched_rt_entity::back to under the
>> CONFIG_RT_GROUP_SCHED block
> This one sure.