From: Tejun Heo <tj@kernel.org>
To: Andrea Righi <arighi@nvidia.com>
Cc: sched-ext@lists.linux.dev, David Vernet <void@manifault.com>,
Changwoo Min <changwoo@igalia.com>,
Emil Tsalapatis <emil@etsalapatis.com>,
David Dai <david.dai@linux.dev>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 17/17] sched_ext: Fix queued bypassed tasks stalling when the host loses SCX_CAP_BASE
Date: Mon, 26 Oct 2026 11:31:30 -1000 [thread overview]
Message-ID: <f8a9aa002627467080c0a3f15c54a28f@kernel.org> (raw)
In-Reply-To: <at4kd-78BbpBX-_4@gpd4>
Hello, Andrea.
On Sun, Oct 25, 2026 at 04:47:03PM +0100, Andrea Righi wrote:
> Not a blocker, but I was wondering if we should preserve the old head or
> ordinary balancing when the donor still holds BASE?
>
> If a selected donee refuses a task homed on the donor, this can put it
> at the tail of the same DSQ. A proxy-migrated blocked donor is refused
> by remote CPUs, so repeated balancing passes could keep pushing it back.
Yeah, the reenqueue at home pushes such a task to the back of its own DSQ
on every pass. Rather than restoring the head put-back, v4 has the walk
skip the task from the start. A balancing donor tests whether the task
can move to the picked donee and leaves it where it is if it can't, as it
already does for a task with no donee. The test is factored into
bypass_lb_can_move(), shared with bypass_lb_move(). A drain still sends
the task home.
If something changes while the move is in flight, the task is still
reenqueued at home and appended to the tail. That's rare enough and not
systemic, so it isn't a problem.
Thanks.
--
tejun
next prev parent reply other threads:[~2026-10-26 21:31 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-23 17:55 [PATCHSET v3 sched_ext/for-7.4] sched_ext: Fix bypassed sub-scheduler tasks stalling when the host lacks caps Tejun Heo
2026-10-23 17:55 ` [PATCH 01/17] sched_ext: Pack scx_ent_flags' multi-bit fields at the top Tejun Heo
2026-10-23 17:55 ` [PATCH 02/17] sched_ext: Clear holding_cpu where the claim is confirmed Tejun Heo
2026-10-23 17:55 ` [PATCH 03/17] sched_ext: Fix bypassed tasks stranded by the reenqueue limit Tejun Heo
2026-10-23 17:55 ` [PATCH 04/17] sched_ext: Fix bypassed tasks looping on a host without SCX_CAP_ENQ Tejun Heo
2026-10-23 17:55 ` [PATCH 05/17] sched_ext: Move refill_task_slice_dfl() below apply_slice_vtime() Tejun Heo
2026-10-23 17:55 ` [PATCH 06/17] sched_ext: Fix rescue served time disagreeing with the slice under proxy execution Tejun Heo
2026-10-23 17:55 ` [PATCH 07/17] sched_ext: Restore a rescuee's slice after ops.stopping() Tejun Heo
2026-10-23 17:55 ` [PATCH 08/17] sched_ext: Fix a cpu idling with a runnable rescuee Tejun Heo
2026-10-23 17:56 ` [PATCH 09/17] sched_ext: Mark the rescue grant as a kernel slice with SCX_TASK_KERNEL_SLICE Tejun Heo
2026-10-23 17:56 ` [PATCH 10/17] sched_ext: Refuse extending a kernel slice Tejun Heo
2026-10-23 17:56 ` [PATCH 11/17] sched_ext: Fix a cpu idling after put_prev_task_scx() queues its task on the local DSQ Tejun Heo
2026-10-23 17:56 ` [PATCH 12/17] sched_ext: Expire prev's slice in dispatch_one() under bypass Tejun Heo
2026-10-23 17:56 ` [PATCH 13/17] sched_ext: Fix bypassed tasks stalling when the host lacks SCX_CAP_BASE Tejun Heo
2026-10-23 17:56 ` [PATCH 14/17] sched_ext: Fix the bypass load balancer stranding tasks on cpus where " Tejun Heo
2026-10-23 17:56 ` [PATCH 15/17] sched_ext: Factor out bypass_lb_move() and insert with the donor DSQ unlocked Tejun Heo
2026-10-23 17:56 ` [PATCH 16/17] sched_ext: Let the bypass load balancer move tasks homed on other cpus Tejun Heo
2026-10-23 17:56 ` [PATCH 17/17] sched_ext: Fix queued bypassed tasks stalling when the host loses SCX_CAP_BASE Tejun Heo
2026-10-25 15:47 ` Andrea Righi
2026-10-26 21:31 ` Tejun Heo [this message]
2026-10-23 20:06 ` [PATCH 18/17] sched_ext: Fix use-after-free of a NONE rescuee leaving sched_ext Tejun Heo
2026-10-23 20:06 ` [PATCH 19/17] sched_ext: Fix the stall watchdog blaming a bypassing owner for a stuck task Tejun Heo
2026-10-25 15:52 ` Andrea Righi
2026-10-26 21:31 ` Tejun Heo
2026-10-23 20:10 ` [PATCH 20/17] sched_ext: Fix a lone IMMED task waiting behind a kept prev Tejun Heo
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