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    SubjectRE: [PATCH] sched/fair: fix pick_eevdf to always find the correct se
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    Hi Chen Yu,

    > Subject: Re: [PATCH] sched/fair: fix pick_eevdf to always find the correct
    > se
    >
    > On 2023-10-06 at 21:24:45 +0200, Peter Zijlstra wrote:
    > > On Fri, Oct 06, 2023 at 05:55:01PM +0200, Peter Zijlstra wrote:
    > >
    > > > And yeah, min_deadline is hosed somehow.
    > > >
    > > > migration/28-185 [028] d..2. 70.264274: validate_cfs_rq: --- /
    > > > migration/28-185 [028] d..2. 70.264277: __print_se:
    > ffff88845cf48080 w: 1024 ve: -58857638 lag: 870381 vd: -55861854 vmd: -
    > 66302085 E (11372/tr)
    > > > migration/28-185 [028] d..2. 70.264280: __print_se:
    > ffff88810d165800 w: 25 ve: -80323686 lag: 22336429 vd: -41496434 vmd: -
    > 66302085 E (-1//autogroup-31)
    > > > migration/28-185 [028] d..2. 70.264282: __print_se:
    > ffff888108379000 w: 25 ve: 0 lag: -57987257 vd: 114632828 vmd: 114632828 N
    > (-1//autogroup-33)
    > > > migration/28-185 [028] d..2. 70.264283: validate_cfs_rq:
    > min_deadline: -55861854 avg_vruntime: -62278313462 / 1074 = -57987256
    > > >
    > > > I need to go make dinner (kids hungry), but I'll see if I can figure
    > > > out how this happens...
    > >
    > > *sigh*, does the below help?
    > >
    > > ---
    > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index
    > > 04fbcbda97d5..6a670f119efa 100644
    > > --- a/kernel/sched/fair.c
    > > +++ b/kernel/sched/fair.c
    > > @@ -3632,6 +3747,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq,
    > struct sched_entity *se,
    > > */
    > > deadline = div_s64(deadline * old_weight, weight);
    > > se->deadline = se->vruntime + deadline;
    > > + min_deadline_cb_propagate(&se->run_node, NULL);
    > > }
    > >
    > > #ifdef CONFIG_SMP
    >
    > Is it because without this patch, the se->deadline is not always synced
    > with se->min_deadline, then in pick_eevdf() the following condition could
    > not be met, thus we get a NULL candidate and has to pick the leftmost one?
    > if (se->deadline == se->min_deadline)
    >
    > Regarding the circular locking warning triggered by printk, does it mean we
    > should not get a NULL candidate from __pick_eevdf() in theory? And besides,
    > we should not use printk with rq lock hold?

    Is it not a useful error log? At least from the initial report Marek Szyprowski doesn't see "EEVDF scheduling fail, picking leftmost" but seen only warning triggered by this in the logs.

    Cheers,
    Biju

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