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Message-ID: <af394d1c-1a13-4322-ba79-913193a1b5e0@huaweicloud.com>
Date: Tue, 4 Nov 2025 10:21:11 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>, Michal Koutný
<mkoutny@...e.com>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
Chen Ridong <chenridong@...wei.com>, Gabriele Monaco <gmonaco@...hat.com>,
Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [cgroup/for-6.19 PATCH v2 3/3] cgroup/cpuset: Globally track
isolated_cpus update
On 2025/11/4 9:30, Waiman Long wrote:
> The current cpuset code passes a local isolcpus_updated flag around in a
> number of functions to determine if external isolation related cpumasks
> like wq_unbound_cpumask should be updated. It is a bit cumbersome and
> makes the code more complex. Simplify the code by using a global boolean
> flag "isolated_cpus_updating" to track this. This flag will be set in
> isolated_cpus_update() and cleared in update_isolation_cpumasks().
>
> No functional change is expected.
>
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
> kernel/cgroup/cpuset.c | 73 ++++++++++++++++++++----------------------
> 1 file changed, 35 insertions(+), 38 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 0c49905df394..854fe4cc1358 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -81,6 +81,13 @@ static cpumask_var_t subpartitions_cpus;
> */
> static cpumask_var_t isolated_cpus;
>
> +/*
> + * isolated_cpus updating flag (protected by cpuset_mutex)
> + * Set if isolated_cpus is going to be updated in the current
> + * cpuset_mutex crtical section.
> + */
> +static bool isolated_cpus_updating;
> +
> /*
> * Housekeeping (HK_TYPE_DOMAIN) CPUs at boot
> */
> @@ -1327,6 +1334,8 @@ static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus
> cpumask_or(isolated_cpus, isolated_cpus, xcpus);
> else
> cpumask_andnot(isolated_cpus, isolated_cpus, xcpus);
> +
> + isolated_cpus_updating = true;
> }
>
> /*
> @@ -1334,15 +1343,12 @@ static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus
> * @new_prs: new partition_root_state
> * @parent: parent cpuset
> * @xcpus: exclusive CPUs to be added
> - * Return: true if isolated_cpus modified, false otherwise
> *
> * Remote partition if parent == NULL
> */
> -static bool partition_xcpus_add(int new_prs, struct cpuset *parent,
> +static void partition_xcpus_add(int new_prs, struct cpuset *parent,
> struct cpumask *xcpus)
> {
> - bool isolcpus_updated;
> -
> WARN_ON_ONCE(new_prs < 0);
> lockdep_assert_held(&callback_lock);
> if (!parent)
> @@ -1352,13 +1358,11 @@ static bool partition_xcpus_add(int new_prs, struct cpuset *parent,
> if (parent == &top_cpuset)
> cpumask_or(subpartitions_cpus, subpartitions_cpus, xcpus);
>
> - isolcpus_updated = (new_prs != parent->partition_root_state);
> - if (isolcpus_updated)
> + if (new_prs != parent->partition_root_state)
> isolated_cpus_update(parent->partition_root_state, new_prs,
> xcpus);
>
> cpumask_andnot(parent->effective_cpus, parent->effective_cpus, xcpus);
> - return isolcpus_updated;
> }
>
> /*
> @@ -1366,15 +1370,12 @@ static bool partition_xcpus_add(int new_prs, struct cpuset *parent,
> * @old_prs: old partition_root_state
> * @parent: parent cpuset
> * @xcpus: exclusive CPUs to be removed
> - * Return: true if isolated_cpus modified, false otherwise
> *
> * Remote partition if parent == NULL
> */
> -static bool partition_xcpus_del(int old_prs, struct cpuset *parent,
> +static void partition_xcpus_del(int old_prs, struct cpuset *parent,
> struct cpumask *xcpus)
> {
> - bool isolcpus_updated;
> -
> WARN_ON_ONCE(old_prs < 0);
> lockdep_assert_held(&callback_lock);
> if (!parent)
> @@ -1383,14 +1384,12 @@ static bool partition_xcpus_del(int old_prs, struct cpuset *parent,
> if (parent == &top_cpuset)
> cpumask_andnot(subpartitions_cpus, subpartitions_cpus, xcpus);
>
> - isolcpus_updated = (old_prs != parent->partition_root_state);
> - if (isolcpus_updated)
> + if (old_prs != parent->partition_root_state)
> isolated_cpus_update(old_prs, parent->partition_root_state,
> xcpus);
>
> cpumask_and(xcpus, xcpus, cpu_active_mask);
> cpumask_or(parent->effective_cpus, parent->effective_cpus, xcpus);
> - return isolcpus_updated;
> }
>
> /*
> @@ -1432,17 +1431,24 @@ static bool isolated_cpus_can_update(struct cpumask *add_cpus,
> return res;
> }
>
> -static void update_isolation_cpumasks(bool isolcpus_updated)
> +/*
> + * update_isolation_cpumasks - Update external isolation related CPU masks
> + *
> + * The following external CPU masks will be updated if necessary:
> + * - workqueue unbound cpumask
> + */
> +static void update_isolation_cpumasks(void)
> {
> int ret;
>
> - lockdep_assert_cpus_held();
> -
> - if (!isolcpus_updated)
> + if (!isolated_cpus_updating)
> return;
>
> + lockdep_assert_cpus_held();
> +
> ret = workqueue_unbound_exclude_cpumask(isolated_cpus);
> WARN_ON_ONCE(ret < 0);
> + isolated_cpus_updating = false;
> }
>
> /**
> @@ -1567,8 +1573,6 @@ static inline bool is_local_partition(struct cpuset *cs)
> static int remote_partition_enable(struct cpuset *cs, int new_prs,
> struct tmpmasks *tmp)
> {
> - bool isolcpus_updated;
> -
> /*
> * The user must have sysadmin privilege.
> */
> @@ -1595,11 +1599,11 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
> return PERR_HKEEPING;
>
> spin_lock_irq(&callback_lock);
> - isolcpus_updated = partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
> + partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
> list_add(&cs->remote_sibling, &remote_children);
> cpumask_copy(cs->effective_xcpus, tmp->new_cpus);
> spin_unlock_irq(&callback_lock);
> - update_isolation_cpumasks(isolcpus_updated);
> + update_isolation_cpumasks();
> cpuset_force_rebuild();
> cs->prs_err = 0;
>
> @@ -1622,15 +1626,12 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
> */
> static void remote_partition_disable(struct cpuset *cs, struct tmpmasks *tmp)
> {
> - bool isolcpus_updated;
> -
> WARN_ON_ONCE(!is_remote_partition(cs));
> WARN_ON_ONCE(!cpumask_subset(cs->effective_xcpus, subpartitions_cpus));
>
> spin_lock_irq(&callback_lock);
> list_del_init(&cs->remote_sibling);
> - isolcpus_updated = partition_xcpus_del(cs->partition_root_state,
> - NULL, cs->effective_xcpus);
> + partition_xcpus_del(cs->partition_root_state, NULL, cs->effective_xcpus);
> if (cs->prs_err)
> cs->partition_root_state = -cs->partition_root_state;
> else
> @@ -1640,7 +1641,7 @@ static void remote_partition_disable(struct cpuset *cs, struct tmpmasks *tmp)
> compute_excpus(cs, cs->effective_xcpus);
> reset_partition_data(cs);
> spin_unlock_irq(&callback_lock);
> - update_isolation_cpumasks(isolcpus_updated);
> + update_isolation_cpumasks();
> cpuset_force_rebuild();
>
> /*
> @@ -1665,7 +1666,6 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
> {
> bool adding, deleting;
> int prs = cs->partition_root_state;
> - int isolcpus_updated = 0;
>
> if (WARN_ON_ONCE(!is_remote_partition(cs)))
> return;
> @@ -1701,9 +1701,9 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
>
> spin_lock_irq(&callback_lock);
> if (adding)
> - isolcpus_updated += partition_xcpus_add(prs, NULL, tmp->addmask);
> + partition_xcpus_add(prs, NULL, tmp->addmask);
> if (deleting)
> - isolcpus_updated += partition_xcpus_del(prs, NULL, tmp->delmask);
> + partition_xcpus_del(prs, NULL, tmp->delmask);
> /*
> * Need to update effective_xcpus and exclusive_cpus now as
> * update_sibling_cpumasks() below may iterate back to the same cs.
> @@ -1712,7 +1712,7 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
> if (xcpus)
> cpumask_copy(cs->exclusive_cpus, xcpus);
> spin_unlock_irq(&callback_lock);
> - update_isolation_cpumasks(isolcpus_updated);
> + update_isolation_cpumasks();
> if (adding || deleting)
> cpuset_force_rebuild();
>
> @@ -1793,7 +1793,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
> int deleting; /* Deleting cpus from parent's effective_cpus */
> int old_prs, new_prs;
> int part_error = PERR_NONE; /* Partition error? */
> - int isolcpus_updated = 0;
> struct cpumask *xcpus = user_xcpus(cs);
> int parent_prs = parent->partition_root_state;
> bool nocpu;
> @@ -2072,14 +2071,12 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
> * and vice versa.
> */
> if (adding)
> - isolcpus_updated += partition_xcpus_del(old_prs, parent,
> - tmp->addmask);
> + partition_xcpus_del(old_prs, parent, tmp->addmask);
> if (deleting)
> - isolcpus_updated += partition_xcpus_add(new_prs, parent,
> - tmp->delmask);
> + partition_xcpus_add(new_prs, parent, tmp->delmask);
>
> spin_unlock_irq(&callback_lock);
> - update_isolation_cpumasks(isolcpus_updated);
> + update_isolation_cpumasks();
>
> if ((old_prs != new_prs) && (cmd == partcmd_update))
> update_partition_exclusive_flag(cs, new_prs);
> @@ -3102,7 +3099,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
> else if (isolcpus_updated)
> isolated_cpus_update(old_prs, new_prs, cs->effective_xcpus);
> spin_unlock_irq(&callback_lock);
> - update_isolation_cpumasks(isolcpus_updated);
> + update_isolation_cpumasks();
>
> /* Force update if switching back to member & update effective_xcpus */
> update_cpumasks_hier(cs, &tmpmask, !new_prs);
Reviewed-by: Chen Ridong <chenridong@...wei.com>
--
Best regards,
Ridong
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