The following commit has been merged into the sched/core branch of tip:
Commit-ID: 4b26cfdd395638918e370f62bd2c33e6f63ffb5e
Gitweb: https://git.kernel.org/tip/4b26cfdd395638918e370f62bd2c33e6f63ffb5e
Author: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 27 May 2024 14:06:53 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 29 Jul 2024 12:22:36 +02:00
sched/core: Fix priority checking for DL server picks
In core scheduling, a DL server pick (which is CFS task) should be
given higher priority than tasks in other classes.
Not doing so causes CFS starvation. A kselftest is added later to
demonstrate this. A CFS task that is competing with RT tasks can
be completely starved without this and the DL server's boosting
completely ignored.
Fix these problems.
Reported-by: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Signed-off-by: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Vineeth Pillai <vineeth@xxxxxxxxxxxxxxx>
Tested-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Link: https://lore.kernel.org/r/48b78521d86f3b33c24994d843c1aad6b987dda9.1716811044.git.bristot@xxxxxxxxxx
---
kernel/sched/core.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f95600c..11abfcd 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -163,6 +163,9 @@ static inline int __task_prio(const struct task_struct *p)
if (p->sched_class == &stop_sched_class) /* trumps deadline */
return -2;
+ if (p->dl_server)
+ return -1; /* deadline */
+
if (rt_prio(p->prio)) /* includes deadline */
return p->prio; /* [-1, 99] */
@@ -192,8 +195,24 @@ static inline bool prio_less(const struct task_struct *a,
if (-pb < -pa)
return false;
- if (pa == -1) /* dl_prio() doesn't work because of stop_class above */
- return !dl_time_before(a->dl.deadline, b->dl.deadline);
+ if (pa == -1) { /* dl_prio() doesn't work because of stop_class above */
+ const struct sched_dl_entity *a_dl, *b_dl;
+
+ a_dl = &a->dl;
+ /*
+ * Since,'a' and 'b' can be CFS tasks served by DL server,
+ * __task_prio() can return -1 (for DL) even for those. In that
+ * case, get to the dl_server's DL entity.
+ */
+ if (a->dl_server)
+ a_dl = a->dl_server;
+
+ b_dl = &b->dl;
+ if (b->dl_server)
+ b_dl = b->dl_server;
+
+ return !dl_time_before(a_dl->deadline, b_dl->deadline);
+ }
if (pa == MAX_RT_PRIO + MAX_NICE) /* fair */
return cfs_prio_less(a, b, in_fi);
|