In RTDS, removing the last eligible pCPU can kill repl_timer. When a pCPU is later re-added, rt_switch_sched() reinitializes the timer object, but pending entries may already exist in replq. Without re-arming from replq head, replenishment can remain inactive until some unrelated event programs the timer again. This may stall budget replenishment for non-extratime units. Fix this by re-arming repl_timer in rt_switch_sched() immediately after init_timer() when replq is non-empty, using the earliest pending deadline. This keeps behavior unchanged when replq is empty. Add a lightweight regression script, test_rtds_repl_timer_rearm.sh, to verify source-level guards and model the expected re-arm decision logic. Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com> --- xen/common/sched/rt.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/xen/common/sched/rt.c b/xen/common/sched/rt.c index XXXXXXX..XXXXXXX 100644 --- a/xen/common/sched/rt.c +++ b/xen/common/sched/rt.c @@ -XXX,XX +XXX,XX @@ rt_switch_sched(struct scheduler *new_ops, unsigned int cpu, if ( prv->repl_timer.status == TIMER_STATUS_invalid || prv->repl_timer.status == TIMER_STATUS_killed ) { + struct list_head *replq = rt_replq(new_ops); + init_timer(&prv->repl_timer, repl_timer_handler, (void *)new_ops, cpu); dprintk(XENLOG_DEBUG, "RTDS: timer initialized on cpu %u\n", cpu); + + /* + * When re-adding CPUs after all RTDS CPUs were removed, replq may + * already contain pending replenishment events. Re-arm immediately. + */ + if ( !list_empty(replq) ) + set_timer(&prv->repl_timer, replq_elem(replq->next)->cur_deadline); } sched_idle_unit(cpu)->priv = vdata; -- 2.43.0 base-commit: a7bf8ff218ca05eb3674fdfd2817f6cff471e96a In RTDS, removing the last eligible pCPU can kill repl_timer. When a pCPU is later re-added, rt_switch_sched() reinitializes the timer object, but pending entries may already exist in replq. Without re-arming from replq head, replenishment can remain inactive until some unrelated event programs the timer again. This may stall budget replenishment for non-extratime units. Fix this by re-arming repl_timer in rt_switch_sched() immediately after init_timer() when replq is non-empty, using the earliest pending deadline. This keeps behavior unchanged when replq is empty. Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com> --- Changes in v2: - update commit description, remove unneeded paragraph xen/common/sched/rt.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/xen/common/sched/rt.c b/xen/common/sched/rt.c index XXXXXXX..XXXXXXX 100644 --- a/xen/common/sched/rt.c +++ b/xen/common/sched/rt.c @@ -XXX,XX +XXX,XX @@ rt_switch_sched(struct scheduler *new_ops, unsigned int cpu, if ( prv->repl_timer.status == TIMER_STATUS_invalid || prv->repl_timer.status == TIMER_STATUS_killed ) { + struct list_head *replq = rt_replq(new_ops); + init_timer(&prv->repl_timer, repl_timer_handler, (void *)new_ops, cpu); dprintk(XENLOG_DEBUG, "RTDS: timer initialized on cpu %u\n", cpu); + + /* + * When re-adding CPUs after all RTDS CPUs were removed, replq may + * already contain pending replenishment events. Re-arm immediately. + */ + if ( !list_empty(replq) ) + set_timer(&prv->repl_timer, replq_elem(replq->next)->cur_deadline); } sched_idle_unit(cpu)->priv = vdata; -- 2.43.0 base-commit: a7bf8ff218ca05eb3674fdfd2817f6cff471e96a