[PATCH v2 9/9] sched,fair: Alternative sched_slice()

From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, mgorman@suse.de, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, bristot@redhat.com,
	joshdon@google.com, valentin.schneider@arm.com
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	greg@kroah.com, linux@rasmusvillemoes.dk
Subject: [PATCH v2 9/9] sched,fair: Alternative sched_slice()
Date: Mon, 12 Apr 2021 12:14:30 +0200	[thread overview]
Message-ID: <20210412102001.611897312@infradead.org> (raw)
In-Reply-To: 20210412101421.609526370@infradead.org

The current sched_slice() seems to have issues; there's two possible
things that could be improved:

 - the 'nr_running' used for __sched_period() is daft when cgroups are
   considered. Using the RQ wide h_nr_running seems like a much more
   consistent number.

 - (esp) cgroups can slice it real fine, which makes for easy
   over-scheduling, ensure min_gran is what the name says.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/fair.c     |   12 +++++++++++-
 kernel/sched/features.h |    3 +++
 2 files changed, 14 insertions(+), 1 deletion(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -680,7 +680,13 @@ static u64 __sched_period(unsigned long
  */
 static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);
+	unsigned int nr_running = cfs_rq->nr_running;
+	u64 slice;
+
+	if (sched_feat(ALT_PERIOD))
+		nr_running = rq_of(cfs_rq)->cfs.h_nr_running;
+
+	slice = __sched_period(nr_running + !se->on_rq);
 
 	for_each_sched_entity(se) {
 		struct load_weight *load;
@@ -697,6 +703,10 @@ static u64 sched_slice(struct cfs_rq *cf
 		}
 		slice = __calc_delta(slice, se->load.weight, load);
 	}
+
+	if (sched_feat(BASE_SLICE))
+		slice = min(slice, (u64)sysctl_sched_min_granularity);
+
 	return slice;
 }
 
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -90,3 +90,6 @@ SCHED_FEAT(WA_BIAS, true)
  */
 SCHED_FEAT(UTIL_EST, true)
 SCHED_FEAT(UTIL_EST_FASTUP, true)
+
+SCHED_FEAT(ALT_PERIOD, true)
+SCHED_FEAT(BASE_SLICE, true)


