From: Valentin Schneider <valentin.schneider@arm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@redhat.com, peterz@infradead.org,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com
Subject: [RFC PATCH 6/7] sched/fair: Split select_task_rq_fair want_affine logic
Date: Wed, 11 Dec 2019 16:44:00 +0000 [thread overview]
Message-ID: <20191211164401.5013-7-valentin.schneider@arm.com> (raw)
In-Reply-To: <20191211164401.5013-1-valentin.schneider@arm.com>
The domain loop within select_task_rq_fair() depends on a few bits of
input, namely the SD flag we're looking for and whether we want_affine.
For !want_affine, the domain loop will walk up the hierarchy to reach the
highest domain with both SD_LOAD_BALANCE and the requested sd_flag
(SD_BALANCE_{WAKE, FORK, EXEC}) set.
In other words, that's a call to highest_flags_domain() for these two
flags. Note that this is a static information wrt a given SD hierarchy,
so we can cache that - but that comes in a later patch to ease reviewing.
For want_affine, we'll walk up the hierarchy to reach the first domain
with SD_LOAD_BALANCE, SD_WAKE_AFFINE, and that spans the tasks's prev_cpu.
We still save a pointer to the last visited domain that had the requested
sd_flag set (and SD_LOAD_BALANCE), which means that if we fail to go
through the affine condition (e.g. no domain had SD_WAKE_AFFINE) we'll use
the same SD as we would have found if we had !want_affine.
Split the domain loop in !want_affine and want_affine paths. As it is,
this leads to two domain walks instead of a single one, but stay tuned for
the next patch.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
kernel/sched/fair.c | 29 ++++++++++++++++++-----------
1 file changed, 18 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 30e8d357a24f..ea875c7c82d7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6370,29 +6370,36 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
}
rcu_read_lock();
+
+ sd = highest_flags_domain(cpu, sd_flag | SD_LOAD_BALANCE);
+
+ /*
+ * If !want_affine, we just look for the highest domain where
+ * sd_flag is set.
+ */
+ if (!want_affine)
+ goto scan;
+
+ /*
+ * Otherwise we look for the lowest domain with SD_WAKE_AFFINE and that
+ * spans both 'cpu' and 'prev_cpu'.
+ */
for_each_domain(cpu, tmp) {
if (!(tmp->flags & SD_LOAD_BALANCE))
break;
- /*
- * If both 'cpu' and 'prev_cpu' are part of this domain,
- * cpu is a valid SD_WAKE_AFFINE target.
- */
- if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
+ if ((tmp->flags & SD_WAKE_AFFINE) &&
cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
if (cpu != prev_cpu)
new_cpu = wake_affine(tmp, p, cpu, prev_cpu, sync);
- sd = NULL; /* Prefer wake_affine over balance flags */
+ /* Prefer wake_affine over SD lookup */
+ sd = NULL;
break;
}
-
- if (tmp->flags & sd_flag)
- sd = tmp;
- else if (!want_affine)
- break;
}
+scan:
if (unlikely(sd)) {
/* Slow path */
new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
--
2.24.0
next prev parent reply other threads:[~2019-12-11 16:44 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-11 16:43 [RFC PATCH 0/7] sched: Streamline select_task_rq() & select_task_rq_fair() Valentin Schneider
2019-12-11 16:43 ` [RFC PATCH 1/7] sched: Add WF_TTWU, WF_EXEC wakeup flags Valentin Schneider
2019-12-11 16:43 ` [RFC PATCH 2/7] sched: Kill select_task_rq()'s sd_flag parameter Valentin Schneider
2019-12-11 16:43 ` [RFC PATCH 3/7] sched/fair: find_idlest_group(): Remove unused " Valentin Schneider
2019-12-11 16:43 ` [RFC PATCH 4/7] sched/fair: Dissociate wakeup decisions from SD flag value Valentin Schneider
2019-12-11 16:53 ` Valentin Schneider
2019-12-11 16:43 ` [RFC PATCH 5/7] sched/topology: Make {lowest/highest}_flag_domain() work with > 1 flags Valentin Schneider
2019-12-11 16:44 ` Valentin Schneider [this message]
2019-12-11 16:44 ` [RFC PATCH 7/7] sched/topology: Define and use shortcut pointers for wakeup sd_flag scan Valentin Schneider
2020-01-06 8:10 ` [RFC PATCH 0/7] sched: Streamline select_task_rq() & select_task_rq_fair() Peter Zijlstra
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