linux-kernel - [PATCH] sched_ext: Documentation: Clarify time slice handling in task lifecycle

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250609162342.18790-1-arighi@nvidia.com>
Date: Mon,  9 Jun 2025 18:23:42 +0200
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>
Cc: Jonathan Corbet <corbet@....net>,
	Emily Soto <emilys@...dia.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] sched_ext: Documentation: Clarify time slice handling in task lifecycle

It is not always obvious how a task's time slice can be refilled, either
explicitly from ops.dispatch() or automatically by the sched_ext core,
to skip subsequent ops.enqueue() and ops.dispatch() calls. This
typically happens when the task is the only one running on a CPU.

To make this behavior easier to understand, update the task lifecycle
diagram to explicitly document how time slice handling works in such
cases.

Signed-off-by: Andrea Righi <arighi@...dia.com>
---
 Documentation/scheduler/sched-ext.rst | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/Documentation/scheduler/sched-ext.rst b/Documentation/scheduler/sched-ext.rst
index a1869c38046ed..404fe6126a769 100644
--- a/Documentation/scheduler/sched-ext.rst
+++ b/Documentation/scheduler/sched-ext.rst
@@ -313,16 +313,21 @@ by a sched_ext scheduler:
         ops.runnable();         /* Task becomes ready to run */
 
         while (task is runnable) {
-            if (task is not in a DSQ) {
+            if (task is not in a DSQ && task->scx.slice == 0) {
                 ops.enqueue();  /* Task can be added to a DSQ */
 
-                /* A CPU becomes available */
+                /* Any usable CPU becomes available */
 
                 ops.dispatch(); /* Task is moved to a local DSQ */
             }
             ops.running();      /* Task starts running on its assigned CPU */
-            ops.tick();         /* Called every 1/HZ seconds */
+            while (task->scx.slice > 0 && task is runnable)
+                ops.tick();     /* Called every 1/HZ seconds */
             ops.stopping();     /* Task stops running (time slice expires or wait) */
+
+            /* Task's CPU becomes available */
+
+            ops.dispatch();     /* task->scx.slice can be refilled */
         }
 
         ops.quiescent();        /* Task releases its assigned CPU (wait) */
-- 
2.49.0