From: Kuba Piecuch <jpiecuch@google.com>
To: Tejun Heo <tj@kernel.org>, David Vernet <void@manifault.com>,
Andrea Righi <andrea.righi@linux.dev>,
Changwoo Min <changwoo@igalia.com>
Cc: <linux-kernel@vger.kernel.org>, <sched-ext@lists.linux.dev>,
Peter Zijlstra <peterz@infradead.org>,
Wen-Fang Liu <liuwenfang@honor.com>
Subject: Re: [PATCH v3 3/3] sched_ext: Allow scx_bpf_reenqueue_local() to be called from anywhere
Date: Thu, 27 Nov 2025 10:39:35 +0000 [thread overview]
Message-ID: <DEJEVK0YKMWY.116BVU5P5G91L@google.com> (raw)
In-Reply-To: <7e9b27d70e31c243da3ce77e622b0af5@kernel.org>
On Wed Oct 29, 2025 at 3:49 PM UTC, Tejun Heo wrote:
> Schedulers can now use standard BPF mechanisms like the sched_switch tracepoint
> to detect and handle CPU preemption.
Correct me if I'm wrong, but I think using the sched_switch tracepoint still
leaves us with no preemption notification in the following scenario:
1. An RT task is running on the CPU and blocks.
2. pick_task_scx() briefly drops the rq lock in balance_one() and the RT task
is woken up.
3. SCX sees the enqueue and returns RETRY_TASK from pick_task_scx().
4. The RT task is picked.
5. Since prev == next, we don't enter the is_switch branch in __schedule()
and the sched_switch tracepoint isn't reached.
The BPF scheduler could hook into trace_sched_exit_tp() to work around this,
but that tracepoint seems to be for testing and debugging purposes only.
next prev parent reply other threads:[~2025-11-27 10:39 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-25 0:18 [PATCHSET sched_ext/for-6.19] sched_ext: Deprecate ops.cpu_acquire/release() Tejun Heo
2025-10-25 0:18 ` [PATCH 1/3] sched_ext: Split schedule_deferred() into locked and unlocked variants Tejun Heo
2025-10-25 23:17 ` Emil Tsalapatis
2025-10-25 0:18 ` [PATCH 2/3] sched_ext: Factor out reenq_local() from scx_bpf_reenqueue_local() Tejun Heo
2025-10-25 23:19 ` Emil Tsalapatis
2025-10-25 0:18 ` [PATCH 3/3] sched_ext: Allow scx_bpf_reenqueue_local() to be called from anywhere Tejun Heo
2025-10-25 23:21 ` Emil Tsalapatis
2025-10-27 9:18 ` Peter Zijlstra
2025-10-27 16:00 ` Tejun Heo
2025-10-27 17:49 ` Peter Zijlstra
2025-10-27 18:05 ` Tejun Heo
2025-10-27 18:07 ` Peter Zijlstra
2025-10-27 18:10 ` Peter Zijlstra
2025-10-27 18:17 ` Tejun Heo
2025-10-28 11:01 ` Peter Zijlstra
2025-10-28 17:07 ` Tejun Heo
2025-10-27 18:19 ` [PATCH v2 " Tejun Heo
2025-10-29 10:45 ` Peter Zijlstra
2025-10-29 15:11 ` Tejun Heo
2025-10-29 15:49 ` [PATCH v3 " Tejun Heo
2025-11-27 10:39 ` Kuba Piecuch [this message]
2025-12-02 23:05 ` Tejun Heo
2025-12-11 14:24 ` Kuba Piecuch
2025-12-11 16:17 ` Tejun Heo
2025-12-11 16:20 ` Tejun Heo
2025-12-13 1:16 ` Andrea Righi
2025-12-13 1:18 ` Tejun Heo
2025-10-29 15:31 ` [PATCHSET sched_ext/for-6.19] sched_ext: Deprecate ops.cpu_acquire/release() Tejun Heo
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