Messages in this thread Patch in this message | | | Date | Tue, 17 Aug 2021 17:56:15 -0700 | Subject | [PATCH] sched/core: fix pick_next_task 'max' tracking | From | Josh Don <> |
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For core-sched, pick_next_task will update the 'max' task if there is a cookie mismatch (since in this case the new task must be of higher priority than the current max). However, we fail to update 'max' if we've found a task with a matching cookie and higher priority than 'max'.
This can result in extra iterations on SMT-X machines, where X > 2.
As an example, on a machine with SMT=3, on core 0, SMT-0 might pick the following, in order:
- SMT-0: p1, with cookie A, and priority 10 (max = p1) - SMT-1: p2, with cookie A, and priority 30 (max not updated here) - SMT-2: p3, with cookie B, and priority 20 (max = p2) > invalidate the other picks and retry
Here, we should have instead updated 'max' when picking for SMT-1. Note that this code would eventually have righted itself, since the retry loop would re-pick p2, and update 'max' accordingly. However, this patch avoids the extra round-trip.
Signed-off-by: Josh Don <joshdon@google.com> --- kernel/sched/core.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3431939699dc..110ea7582a33 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5623,6 +5623,8 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) occ = 1; goto again; } + } else if (prio_less(max, p, fi_before)) { + max = p; } } } -- 2.33.0.rc1.237.g0d66db33f3-goog
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