Re: SCHED_DEADLINE tasks missing their deadline with SCHED_FLAG_RECLAIM jobs in the mix (using GRUB)

luca abeni
2025-06-24T15:00:43Z

On Tue, 24 Jun 2025 14:59:13 +0200
Juri Lelli <juri.lelli@redhat.com> wrote:

> Hello again,
>
> On 24/06/25 09:49, Juri Lelli wrote:
>
> ...
>
> > The following seem to at least cure the problem after boot. Things
> > are still broken after cpusets creation. Moving to look into that,
> > but wanted to share where I am so that we don't duplicate work.
>
> I ended up with two additional patches that seem to make things a
> little better at my end. You can find them at
>
> https://github.com/jlelli/linux/tree/upstream/fix-grub
>
> Marcel, Luca, can you please give them a quick try to check if they do
> any good?

I applied your 3 patches to the master branch of linux.git, and they
indeed seems to fix the issue!

Now, I need to understand how they relate to
5f6bd380c7bdbe10f7b4e8ddcceed60ce0714c6d :)

One small issue: after applying your patches, I get this WARN at boot
time:
[ 0.384481] ------------[ cut here ]------------
[ 0.385384] WARNING: CPU: 0 PID: 1 at kernel/sched/deadline.c:265 task_non_contending+0x24d/0x3b0
[ 0.385384] Modules linked in:
[ 0.385384] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.16.0-rc2-00234-ge35a18896578 #42 PREEMPT(voluntary)
[ 0.385384] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 0.385384] RIP: 0010:task_non_contending+0x24d/0x3b0
[ 0.385384] Code: 59 49 00 e9 7a fe ff ff 48 8b 53 30 f6 43 53 10 0f 85 4c ff ff ff 48 8b 85 c8 08 00 00 48 29 d0 48 89 85 c8 08 00 00 73 0f 90 <0f> 0b 90 48 c7 85 c8 08 00 00 00 00 00 00 48 63 95 28 0b 00 00 48
[ 0.385384] RSP: 0000:ffffb52300013c08 EFLAGS: 00010093
[ 0.385384] RAX: ffffffffffff3334 RBX: ffff979ffe8292b0 RCX: 0000000000000001
[ 0.385384] RDX: 000000000000cccc RSI: 0000000002faf080 RDI: ffff979ffe8292b0
[ 0.385384] RBP: ffff979ffe8289c0 R08: 0000000000000001 R09: 00000000000002a5
[ 0.385384] R10: 0000000000000000 R11: 0000000000000001 R12: ffffffffffe0ab69
[ 0.385384] R13: ffff979ffe828a40 R14: 0000000000000009 R15: ffff979ffe8289c0
[ 0.385384] FS: 0000000000000000(0000) GS:ffff97a05f709000(0000) knlGS:0000000000000000
[ 0.385384] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.385384] CR2: ffff979fdec01000 CR3: 000000001e030000 CR4: 00000000000006f0
[ 0.385384] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.385384] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.385384] Call Trace:
[ 0.385384] <TASK>
[ 0.385384] dl_server_stop+0x21/0x40
[ 0.385384] dequeue_entities+0x604/0x900
[ 0.385384] dequeue_task_fair+0x85/0x190
[ 0.385384] ? update_rq_clock+0x6c/0x110
[ 0.385384] __schedule+0x1f0/0xee0
[ 0.385384] schedule+0x22/0xd0
[ 0.385384] schedule_timeout+0xf4/0x100
[ 0.385384] __wait_for_common+0x97/0x180
[ 0.385384] ? __pfx_schedule_timeout+0x10/0x10
[ 0.385384] ? __pfx_devtmpfsd+0x10/0x10
[ 0.385384] wait_for_completion_killable+0x1f/0x40
[ 0.385384] __kthread_create_on_node+0xe7/0x150
[ 0.385384] kthread_create_on_node+0x4f/0x70
[ 0.385384] ? register_filesystem+0x97/0xc0
[ 0.385384] devtmpfs_init+0x115/0x200
[ 0.385384] driver_init+0x15/0x50
[ 0.385384] kernel_init_freeable+0xf4/0x2d0
[ 0.385384] ? __pfx_kernel_init+0x10/0x10
[ 0.385384] kernel_init+0x15/0x1c0
[ 0.385384] ret_from_fork+0x80/0xd0
[ 0.385384] ? __pfx_kernel_init+0x10/0x10
[ 0.385384] ret_from_fork_asm+0x1a/0x30
[ 0.385384] </TASK>
[ 0.385384] ---[ end trace 0000000000000000 ]---

Luca