linux-kernel - [PATCH 4/2] sched/cpupri: Add CPUPRI

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Date:   Wed, 14 Oct 2020 21:54:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 4/2] sched/cpupri: Add CPUPRI_HIGHER


Add CPUPRI_HIGHER above the RT99 priority to denote the CPU is in use
by higher priority tasks (specifically deadline).

XXX: we should probably drive PUSH-PULL from cpupri, that would
automagically result in an RT-PUSH when DL sets cpupri to CPUPRI_HIGHER.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/cpupri.c   |   10 ++++++++--
 kernel/sched/cpupri.h   |    3 ++-
 kernel/sched/deadline.c |    3 +++
 3 files changed, 13 insertions(+), 3 deletions(-)

--- a/kernel/sched/cpupri.c
+++ b/kernel/sched/cpupri.c
@@ -11,7 +11,7 @@
  *  This code tracks the priority of each CPU so that global migration
  *  decisions are easy to calculate.  Each CPU can be in a state as follows:
  *
- *                 (INVALID), NORMAL, RT1, ... RT99
+ *                 (INVALID), NORMAL, RT1, ... RT99, HIGHER
  *
  *  going from the lowest priority to the highest.  CPUs in the INVALID state
  *  are not eligible for routing.  The system maintains this state with
@@ -19,7 +19,7 @@
  *  in that class).  Therefore a typical application without affinity
  *  restrictions can find a suitable CPU with O(1) complexity (e.g. two bit
  *  searches).  For tasks with affinity restrictions, the algorithm has a
- *  worst case complexity of O(min(100, nr_domcpus)), though the scenario that
+ *  worst case complexity of O(min(101, nr_domcpus)), though the scenario that
  *  yields the worst case search is fairly contrived.
  */
 #include "sched.h"
@@ -37,6 +37,8 @@
  *	       50        49       49       50
  *	      ...
  *	       99         0        0       99
+ *
+ *				 100	  100 (CPUPRI_HIGHER)
  */
 static int convert_prio(int prio)
 {
@@ -54,6 +56,10 @@ static int convert_prio(int prio)
 	case MAX_RT_PRIO-1:
 		cpupri = CPUPRI_NORMAL;		/*  0 */
 		break;
+
+	case MAX_RT_PRIO:
+		cpupri = CPUPRI_HIGHER;		/* 100 */
+		break;
 	}

 	return cpupri;
--- a/kernel/sched/cpupri.h
+++ b/kernel/sched/cpupri.h
@@ -1,10 +1,11 @@
 /* SPDX-License-Identifier: GPL-2.0 */

-#define CPUPRI_NR_PRIORITIES	MAX_RT_PRIO
+#define CPUPRI_NR_PRIORITIES	(MAX_RT_PRIO+1)

 #define CPUPRI_INVALID		-1
 #define CPUPRI_NORMAL		 0
 /* values 1-99 are for RT1-RT99 priorities */
+#define CPUPRI_HIGHER		100

 struct cpupri_vec {
 	atomic_t		count;
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1364,6 +1364,8 @@ static void inc_dl_deadline(struct dl_rq

 	if (dl_rq->earliest_dl.curr == 0 ||
 	    dl_time_before(deadline, dl_rq->earliest_dl.curr)) {
+		if (dl_rq->earliest_dl.curr == 0)
+			cpupri_set(&rq->rd->cpupri, rq->cpu, CPUPRI_HIGHER);
 		dl_rq->earliest_dl.curr = deadline;
 		cpudl_set(&rq->rd->cpudl, rq->cpu, deadline);
 	}
@@ -1381,6 +1383,7 @@ static void dec_dl_deadline(struct dl_rq
 		dl_rq->earliest_dl.curr = 0;
 		dl_rq->earliest_dl.next = 0;
 		cpudl_clear(&rq->rd->cpudl, rq->cpu);
+		cpupri_set(&rq->rd->cpupri, rq->cpu, rq->rt.highest_prio.curr);
 	} else {
 		struct rb_node *leftmost = dl_rq->root.rb_leftmost;
 		struct sched_dl_entity *entry;