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Re: [PATCH v3] xen/sched: rtds: assert replq is empty on timer (re-)init
- To: Oleksii Moisieiev <Oleksii_Moisieiev@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jürgen Groß <jgross@xxxxxxxx>
- Date: Mon, 4 May 2026 16:49:01 +0200
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- Cc: Dario Faggioli <dfaggioli@xxxxxxxx>, George Dunlap <gwd@xxxxxxxxxxxxxx>, Meng Xu <mengxu@xxxxxxxxxxxxx>
- Delivery-date: Mon, 04 May 2026 14:49:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 04.05.26 15:40, Oleksii Moisieiev wrote:
In RTDS, removing the last eligible pCPU kills repl_timer. When a pCPU
is later re-added, rt_switch_sched() reinitializes the timer object.
cpupool_unassign_cpu_start() refuses to remove the last pCPU from a
populated cpupool: if any domain is still alive while the system is
active it returns -EBUSY, otherwise all domains are first moved to
cpupool0. Consequently, by the time the killed-timer branch runs, no
units remain in the pool and replq is guaranteed to be empty.
Document this invariant by asserting list_empty(replq) right after
init_timer(). This catches any future regression in cpupool semantics
that would leave pending replenishment events behind across a
TIMER_STATUS_killed -> init_timer() transition, where the timer would
otherwise stay disarmed until an unrelated event reprogrammed it.
Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@xxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Juergen
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