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    Subject[PATCH] sched/core: fix pick_next_task 'max' tracking
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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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