Messages in this thread Patch in this message | | | From | "Joel Fernandes (Google)" <> | Subject | [PATCH v2 03/15] sched/core: Fix priority checking for DL server picks | Date | Tue, 12 Mar 2024 21:24:39 -0400 |
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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.
Reviewed-by: Vineeth Pillai <vineeth@bitbyteword.org> Reported-by: Suleiman Souhlal <suleiman@google.com> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> --- 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 63f41453b79e..0a05caf9d3d7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -162,6 +162,9 @@ 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] */ @@ -191,8 +194,24 @@ 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); -- 2.34.1
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