linux-kernel - Re: [PATCH 1/2] sched/deadline: Restore dl_server bandwidth on non-destructive root domain changes

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Message-Id: <3F3A1712-6F87-444D-A2FA-B009D30CF1BF@joelfernandes.org>
Date: Sun, 17 Nov 2024 09:54:19 +0900
From: Joel Fernandes <joel@...lfernandes.org>
To: Juri Lelli <juri.lelli@...hat.com>
Cc: Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
 Johannes Weiner <hannes@...xchg.org>, Michal Koutny <mkoutny@...e.com>,
 Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Qais Yousef <qyousef@...alina.io>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Suleiman Souhlal <suleiman@...gle.com>,
 Aashish Sharma <shraash@...gle.com>, Shin Kawamura <kawasin@...gle.com>,
 Vineeth Remanan Pillai <vineeth@...byteword.org>,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH 1/2] sched/deadline: Restore dl_server bandwidth on non-destructive root domain changes



> On Nov 13, 2024, at 9:57 PM, Juri Lelli <juri.lelli@...hat.com> wrote:
> 
> When root domain non-destructive changes (e.g., only modifying one of
> the existing root domains while the rest is not touched) happen we still
> need to clear DEADLINE bandwidth accounting so that it's then properly
> restore taking into account DEADLINE tasks associated to each cpuset
> (associated to each root domain). After the introduction of dl_servers,
> we fail to restore such servers contribution after non-destructive
> changes (as they are only considered on destructive changes when
> runqueues are attached to the new domains).
> 
> Fix this by making sure we iterate over the dl_server attached to
> domains that have not been destroyed and add them bandwidth contribution
> back correctly.
> 
> Signed-off-by: Juri Lelli <juri.lelli@...hat.com>

Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>

Thanks,

 - Joel




> ---
> include/linux/sched/deadline.h |  2 +-
> kernel/cgroup/cpuset.c         |  2 +-
> kernel/sched/deadline.c        | 18 +++++++++++++-----
> kernel/sched/topology.c        | 10 ++++++----
> 4 files changed, 21 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/sched/deadline.h b/include/linux/sched/deadline.h
> index 3a912ab42bb5..82c966a55856 100644
> --- a/include/linux/sched/deadline.h
> +++ b/include/linux/sched/deadline.h
> @@ -33,7 +33,7 @@ static inline bool dl_time_before(u64 a, u64 b)
> 
> struct root_domain;
> extern void dl_add_task_root_domain(struct task_struct *p);
> -extern void dl_clear_root_domain(struct root_domain *rd);
> +extern void dl_clear_root_domain(struct root_domain *rd, bool restore);
> 
> #endif /* CONFIG_SMP */
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 142303abb055..4d3603a99db3 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -954,7 +954,7 @@ static void dl_rebuild_rd_accounting(void)
>     * Clear default root domain DL accounting, it will be computed again
>     * if a task belongs to it.
>     */
> -    dl_clear_root_domain(&def_root_domain);
> +    dl_clear_root_domain(&def_root_domain, false);
> 
>    cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 9ce93d0bf452..e53208a50279 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2968,13 +2968,21 @@ void dl_add_task_root_domain(struct task_struct *p)
>    task_rq_unlock(rq, p, &rf);
> }
> 
> -void dl_clear_root_domain(struct root_domain *rd)
> +void dl_clear_root_domain(struct root_domain *rd, bool restore)
> {
> -    unsigned long flags;
> -
> -    raw_spin_lock_irqsave(&rd->dl_bw.lock, flags);
> +    guard(raw_spinlock_irqsave)(&rd->dl_bw.lock);
>    rd->dl_bw.total_bw = 0;
> -    raw_spin_unlock_irqrestore(&rd->dl_bw.lock, flags);
> +
> +    if (restore) {
> +        int i;
> +
> +        for_each_cpu(i, rd->span) {
> +            struct sched_dl_entity *dl_se = &cpu_rq(i)->fair_server;
> +
> +            if (dl_server(dl_se))
> +                rd->dl_bw.total_bw += dl_se->dl_bw;
> +        }
> +    }
> }
> 
> #endif /* CONFIG_SMP */
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 9748a4c8d668..e9e7a7c43dd6 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -2721,12 +2721,14 @@ void partition_sched_domains_locked(int ndoms_new, cpumask_var_t doms_new[],
> 
>                /*
>                 * This domain won't be destroyed and as such
> -                 * its dl_bw->total_bw needs to be cleared.  It
> -                 * will be recomputed in function
> -                 * update_tasks_root_domain().
> +                 * its dl_bw->total_bw needs to be cleared.
> +                 * Tasks contribution will be then recomputed
> +                 * in function dl_update_tasks_root_domain(),
> +                 * dl_servers contribution in function
> +                 * dl_restore_server_root_domain().
>                 */
>                rd = cpu_rq(cpumask_any(doms_cur[i]))->rd;
> -                dl_clear_root_domain(rd);
> +                dl_clear_root_domain(rd, true);
>                goto match1;
>            }
>        }
> --
> 2.47.0
>