add a sched patch to the "next" queue

diff --git a/next/6.15/sched-deadline-less-agressive-dl_server-handling.patch b/next/6.15/sched-deadline-less-agressive-dl_server-handling.patch
new file mode 100644 (file)
index 0000000..0441721
--- /dev/null
+++ b/next/6.15/sched-deadline-less-agressive-dl_server-handling.patch
@@ -0,0 +1,163 @@
+From c0a825f92d92fdccff156fd030efa068df138577 Mon Sep 17 00:00:00 2001
+From: Sasha Levin <sashal@kernel.org>
+Date: Tue, 20 May 2025 11:19:30 +0200
+Subject: sched/deadline: Less agressive dl_server handling
+
+From: Peter Zijlstra <peterz@infradead.org>
+
+[ Upstream commit cccb45d7c4295bbfeba616582d0249f2d21e6df5 ]
+
+Chris reported that commit 5f6bd380c7bd ("sched/rt: Remove default
+bandwidth control") caused a significant dip in his favourite
+benchmark of the day. Simply disabling dl_server cured things.
+
+His workload hammers the 0->1, 1->0 transitions, and the
+dl_server_{start,stop}() overhead kills it -- fairly obviously a bad
+idea in hind sight and all that.
+
+Change things around to only disable the dl_server when there has not
+been a fair task around for a whole period. Since the default period
+is 1 second, this ensures the benchmark never trips this, overhead
+gone.
+
+Fixes: 557a6bfc662c ("sched/fair: Add trivial fair server")
+Reported-by: Chris Mason <clm@meta.com>
+Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
+Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
+Acked-by: Juri Lelli <juri.lelli@redhat.com>
+Link: https://lkml.kernel.org/r/20250702121158.465086194@infradead.org
+Signed-off-by: Sasha Levin <sashal@kernel.org>
+---
+ include/linux/sched.h   |  1 +
+ kernel/sched/deadline.c | 25 ++++++++++++++++++++++---
+ kernel/sched/fair.c     |  9 ---------
+ 3 files changed, 23 insertions(+), 12 deletions(-)
+
+diff --git a/include/linux/sched.h b/include/linux/sched.h
+index f96ac1982893..1f92572b20c0 100644
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -702,6 +702,7 @@ struct sched_dl_entity {
+       unsigned int                    dl_defer          : 1;
+       unsigned int                    dl_defer_armed    : 1;
+       unsigned int                    dl_defer_running  : 1;
++      unsigned int                    dl_server_idle    : 1;
+ 
+       /*
+        * Bandwidth enforcement timer. Each -deadline task has its
+diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
+index 89019a140826..094134c9b135 100644
+--- a/kernel/sched/deadline.c
++++ b/kernel/sched/deadline.c
+@@ -1215,6 +1215,8 @@ static void __push_dl_task(struct rq *rq, struct rq_flags *rf)
+ /* a defer timer will not be reset if the runtime consumed was < dl_server_min_res */
+ static const u64 dl_server_min_res = 1 * NSEC_PER_MSEC;
+ 
++static bool dl_server_stopped(struct sched_dl_entity *dl_se);
++
+ static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_dl_entity *dl_se)
+ {
+       struct rq *rq = rq_of_dl_se(dl_se);
+@@ -1234,6 +1236,7 @@ static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_
+ 
+               if (!dl_se->server_has_tasks(dl_se)) {
+                       replenish_dl_entity(dl_se);
++                      dl_server_stopped(dl_se);
+                       return HRTIMER_NORESTART;
+               }
+ 
+@@ -1639,8 +1642,10 @@ void dl_server_update_idle_time(struct rq *rq, struct task_struct *p)
+ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec)
+ {
+       /* 0 runtime = fair server disabled */
+-      if (dl_se->dl_runtime)
++      if (dl_se->dl_runtime) {
++              dl_se->dl_server_idle = 0;
+               update_curr_dl_se(dl_se->rq, dl_se, delta_exec);
++      }
+ }
+ 
+ void dl_server_start(struct sched_dl_entity *dl_se)
+@@ -1663,7 +1668,7 @@ void dl_server_start(struct sched_dl_entity *dl_se)
+               setup_new_dl_entity(dl_se);
+       }
+ 
+-      if (!dl_se->dl_runtime)
++      if (!dl_se->dl_runtime || dl_se->dl_server_active)
+               return;
+ 
+       dl_se->dl_server_active = 1;
+@@ -1684,6 +1689,20 @@ void dl_server_stop(struct sched_dl_entity *dl_se)
+       dl_se->dl_server_active = 0;
+ }
+ 
++static bool dl_server_stopped(struct sched_dl_entity *dl_se)
++{
++      if (!dl_se->dl_server_active)
++              return false;
++
++      if (dl_se->dl_server_idle) {
++              dl_server_stop(dl_se);
++              return true;
++      }
++
++      dl_se->dl_server_idle = 1;
++      return false;
++}
++
+ void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
+                   dl_server_has_tasks_f has_tasks,
+                   dl_server_pick_f pick_task)
+@@ -2435,7 +2454,7 @@ static struct task_struct *__pick_task_dl(struct rq *rq)
+       if (dl_server(dl_se)) {
+               p = dl_se->server_pick_task(dl_se);
+               if (!p) {
+-                      if (dl_server_active(dl_se)) {
++                      if (!dl_server_stopped(dl_se)) {
+                               dl_se->dl_yielded = 1;
+                               update_curr_dl_se(rq, dl_se, 0);
+                       }
+diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
+index 138d9f4658d5..9746eff2eff7 100644
+--- a/kernel/sched/fair.c
++++ b/kernel/sched/fair.c
+@@ -5886,7 +5886,6 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
+       struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
+       struct sched_entity *se;
+       long queued_delta, runnable_delta, idle_delta, dequeue = 1;
+-      long rq_h_nr_queued = rq->cfs.h_nr_queued;
+ 
+       raw_spin_lock(&cfs_b->lock);
+       /* This will start the period timer if necessary */
+@@ -5970,10 +5969,6 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
+ 
+       /* At this point se is NULL and we are at root level*/
+       sub_nr_running(rq, queued_delta);
+-
+-      /* Stop the fair server if throttling resulted in no runnable tasks */
+-      if (rq_h_nr_queued && !rq->cfs.h_nr_queued)
+-              dl_server_stop(&rq->fair_server);
+ done:
+       /*
+        * Note: distribution will already see us throttled via the
+@@ -7067,7 +7062,6 @@ static void set_next_buddy(struct sched_entity *se);
+ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
+ {
+       bool was_sched_idle = sched_idle_rq(rq);
+-      int rq_h_nr_queued = rq->cfs.h_nr_queued;
+       bool task_sleep = flags & DEQUEUE_SLEEP;
+       bool task_delayed = flags & DEQUEUE_DELAYED;
+       struct task_struct *p = NULL;
+@@ -7151,9 +7145,6 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
+ 
+       sub_nr_running(rq, h_nr_queued);
+ 
+-      if (rq_h_nr_queued && !rq->cfs.h_nr_queued)
+-              dl_server_stop(&rq->fair_server);
+-
+       /* balance early to pull high priority tasks */
+       if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
+               rq->next_balance = jiffies;
+-- 
+2.39.5
+

diff --git a/next/6.16/sched-deadline-less-agressive-dl_server-handling.patch b/next/6.16/sched-deadline-less-agressive-dl_server-handling.patch
new file mode 100644 (file)
index 0000000..4d6e387
--- /dev/null
+++ b/next/6.16/sched-deadline-less-agressive-dl_server-handling.patch
@@ -0,0 +1,163 @@
+From d92f16b1d33db49aad293ba7bb82c53571cc1a2e Mon Sep 17 00:00:00 2001
+From: Sasha Levin <sashal@kernel.org>
+Date: Tue, 20 May 2025 11:19:30 +0200
+Subject: sched/deadline: Less agressive dl_server handling
+
+From: Peter Zijlstra <peterz@infradead.org>
+
+[ Upstream commit cccb45d7c4295bbfeba616582d0249f2d21e6df5 ]
+
+Chris reported that commit 5f6bd380c7bd ("sched/rt: Remove default
+bandwidth control") caused a significant dip in his favourite
+benchmark of the day. Simply disabling dl_server cured things.
+
+His workload hammers the 0->1, 1->0 transitions, and the
+dl_server_{start,stop}() overhead kills it -- fairly obviously a bad
+idea in hind sight and all that.
+
+Change things around to only disable the dl_server when there has not
+been a fair task around for a whole period. Since the default period
+is 1 second, this ensures the benchmark never trips this, overhead
+gone.
+
+Fixes: 557a6bfc662c ("sched/fair: Add trivial fair server")
+Reported-by: Chris Mason <clm@meta.com>
+Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
+Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
+Acked-by: Juri Lelli <juri.lelli@redhat.com>
+Link: https://lkml.kernel.org/r/20250702121158.465086194@infradead.org
+Signed-off-by: Sasha Levin <sashal@kernel.org>
+---
+ include/linux/sched.h   |  1 +
+ kernel/sched/deadline.c | 25 ++++++++++++++++++++++---
+ kernel/sched/fair.c     |  9 ---------
+ 3 files changed, 23 insertions(+), 12 deletions(-)
+
+diff --git a/include/linux/sched.h b/include/linux/sched.h
+index aa9c5be7a632..ae75562cca59 100644
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -701,6 +701,7 @@ struct sched_dl_entity {
+       unsigned int                    dl_defer          : 1;
+       unsigned int                    dl_defer_armed    : 1;
+       unsigned int                    dl_defer_running  : 1;
++      unsigned int                    dl_server_idle    : 1;
+ 
+       /*
+        * Bandwidth enforcement timer. Each -deadline task has its
+diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
+index 89019a140826..094134c9b135 100644
+--- a/kernel/sched/deadline.c
++++ b/kernel/sched/deadline.c
+@@ -1215,6 +1215,8 @@ static void __push_dl_task(struct rq *rq, struct rq_flags *rf)
+ /* a defer timer will not be reset if the runtime consumed was < dl_server_min_res */
+ static const u64 dl_server_min_res = 1 * NSEC_PER_MSEC;
+ 
++static bool dl_server_stopped(struct sched_dl_entity *dl_se);
++
+ static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_dl_entity *dl_se)
+ {
+       struct rq *rq = rq_of_dl_se(dl_se);
+@@ -1234,6 +1236,7 @@ static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_
+ 
+               if (!dl_se->server_has_tasks(dl_se)) {
+                       replenish_dl_entity(dl_se);
++                      dl_server_stopped(dl_se);
+                       return HRTIMER_NORESTART;
+               }
+ 
+@@ -1639,8 +1642,10 @@ void dl_server_update_idle_time(struct rq *rq, struct task_struct *p)
+ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec)
+ {
+       /* 0 runtime = fair server disabled */
+-      if (dl_se->dl_runtime)
++      if (dl_se->dl_runtime) {
++              dl_se->dl_server_idle = 0;
+               update_curr_dl_se(dl_se->rq, dl_se, delta_exec);
++      }
+ }
+ 
+ void dl_server_start(struct sched_dl_entity *dl_se)
+@@ -1663,7 +1668,7 @@ void dl_server_start(struct sched_dl_entity *dl_se)
+               setup_new_dl_entity(dl_se);
+       }
+ 
+-      if (!dl_se->dl_runtime)
++      if (!dl_se->dl_runtime || dl_se->dl_server_active)
+               return;
+ 
+       dl_se->dl_server_active = 1;
+@@ -1684,6 +1689,20 @@ void dl_server_stop(struct sched_dl_entity *dl_se)
+       dl_se->dl_server_active = 0;
+ }
+ 
++static bool dl_server_stopped(struct sched_dl_entity *dl_se)
++{
++      if (!dl_se->dl_server_active)
++              return false;
++
++      if (dl_se->dl_server_idle) {
++              dl_server_stop(dl_se);
++              return true;
++      }
++
++      dl_se->dl_server_idle = 1;
++      return false;
++}
++
+ void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
+                   dl_server_has_tasks_f has_tasks,
+                   dl_server_pick_f pick_task)
+@@ -2435,7 +2454,7 @@ static struct task_struct *__pick_task_dl(struct rq *rq)
+       if (dl_server(dl_se)) {
+               p = dl_se->server_pick_task(dl_se);
+               if (!p) {
+-                      if (dl_server_active(dl_se)) {
++                      if (!dl_server_stopped(dl_se)) {
+                               dl_se->dl_yielded = 1;
+                               update_curr_dl_se(rq, dl_se, 0);
+                       }
+diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
+index 7a14da5396fb..3ab8d4765edd 100644
+--- a/kernel/sched/fair.c
++++ b/kernel/sched/fair.c
+@@ -5889,7 +5889,6 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
+       struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
+       struct sched_entity *se;
+       long queued_delta, runnable_delta, idle_delta, dequeue = 1;
+-      long rq_h_nr_queued = rq->cfs.h_nr_queued;
+ 
+       raw_spin_lock(&cfs_b->lock);
+       /* This will start the period timer if necessary */
+@@ -5973,10 +5972,6 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
+ 
+       /* At this point se is NULL and we are at root level*/
+       sub_nr_running(rq, queued_delta);
+-
+-      /* Stop the fair server if throttling resulted in no runnable tasks */
+-      if (rq_h_nr_queued && !rq->cfs.h_nr_queued)
+-              dl_server_stop(&rq->fair_server);
+ done:
+       /*
+        * Note: distribution will already see us throttled via the
+@@ -7070,7 +7065,6 @@ static void set_next_buddy(struct sched_entity *se);
+ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
+ {
+       bool was_sched_idle = sched_idle_rq(rq);
+-      int rq_h_nr_queued = rq->cfs.h_nr_queued;
+       bool task_sleep = flags & DEQUEUE_SLEEP;
+       bool task_delayed = flags & DEQUEUE_DELAYED;
+       struct task_struct *p = NULL;
+@@ -7154,9 +7148,6 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
+ 
+       sub_nr_running(rq, h_nr_queued);
+ 
+-      if (rq_h_nr_queued && !rq->cfs.h_nr_queued)
+-              dl_server_stop(&rq->fair_server);
+-
+       /* balance early to pull high priority tasks */
+       if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
+               rq->next_balance = jiffies;
+-- 
+2.39.5
+