Subject: Re: [PATCH] sched/fair: fix pick_eevdf to always find the correct se
Date: Wed, 4 Oct 2023 22:39:39 +0200 [thread overview]
Message-ID: <c92bc8a6-225d-4fd2-88b5-8994090fb2de@xxxxxxxxxxx> (raw)
In-Reply-To: <xm261qego72d.fsf_-_@xxxxxxxxxx>
Hi,
On 30.09.2023 02:09, Benjamin Segall wrote:
> The old pick_eevdf could fail to find the actual earliest eligible
> deadline when it descended to the right looking for min_deadline, but it
> turned out that that min_deadline wasn't actually eligible. In that case
> we need to go back and search through any left branches we skipped
> looking for the actual best _eligible_ min_deadline.
>
> This is more expensive, but still O(log n), and at worst should only
> involve descending two branches of the rbtree.
>
> I've run this through a userspace stress test (thank you
> tools/lib/rbtree.c), so hopefully this implementation doesn't miss any
> corner cases.
>
> Fixes: 147f3efaa241 ("sched/fair: Implement an EEVDF-like scheduling policy")
> Signed-off-by: Ben Segall <bsegall@xxxxxxxxxx>
This patch causing issues [1] in Renesas RZ/G2L SMARC EVK platform. Reverting the patch fixes the warning messages
[1]
[ 25.550898] EEVDF scheduling fail, picking leftmost
[ 15.109634] ======================================================
[ 15.109636] WARNING: possible circular locking dependency detected
[ 15.109641] 6.6.0-rc4-next-20231005-arm64-renesas-ga03f9ebbbb4c #1165 Not tainted
[ 15.109648] ------------------------------------------------------
[ 15.109649] migration/0/16 is trying to acquire lock:
[ 15.109654] ffff800081713460 (console_owner){..-.}-{0:0}, at: console_flush_all.constprop.0+0x1a0/0x438
[ 15.109694]
[ 15.109694] but task is already holding lock:
[ 15.109697] ffff00007fbd2298 (&rq->__lock){-.-.}-{2:2}, at: __schedule+0xd0/0xbe0
[ 15.109718]
[ 15.109718] which lock already depends on the new lock.
[ 15.109718]
[ 15.109720]
[ 15.109720] the existing dependency chain (in reverse order) is:
25.551560] __down_trylock_console_sem+0x34/0xb8
[ 25.551567] console_trylock+0x24/0x74
[ 25.551574] vprintk_emit+0x114/0x388
[ 25.551581] vprintk_default+0x34/0x3c
[ 25.551588] vprintk+0x9c/0xb4
[ 25.551594] _printk+0x58/0x7c
[ 25.551600] pick_next_task_fair+0x274/0x480
[ 25.551608] __schedule+0x154/0xbe0
[ 25.551616] schedule+0x48/0x110
[ 25.551623] worker_thread+0x1b8/0x3f8
[ 25.551630] kthread+0x114/0x118
[ 25.551635] ret_from_fork+0x10/0x20
[ OK ] Started System Logging Service.
[ 26.099203] EEVDF scheduling fail, picking leftmost
Cheers,
Biju
