On 2026/1/2 3:15, Waiman Long wrote:
> Currently, when setting a cpuset's cpuset.cpus to a value that conflicts
> with the cpuset.cpus/cpuset.cpus.exclusive of a sibling partition,
> the sibling's partition state becomes invalid. This is overly harsh and
> is probably not necessary.
>
> The cpuset.cpus.exclusive control file, if set, will override the
> cpuset.cpus of the same cpuset when creating a cpuset partition.
> So cpuset.cpus has less priority than cpuset.cpus.exclusive in setting up
> a partition. However, it cannot override a conflicting cpuset.cpus file
> in a sibling cpuset and the partition creation process will fail. This
> is inconsistent. That will also make using cpuset.cpus.exclusive less
> valuable as a tool to set up cpuset partitions as the users have to
> check if such a cpuset.cpus conflict exists or not.
>
> Fix these problems by strictly adhering to the setting of the
> following control files in descending order of priority when setting
> up a partition.
>
> 1. cpuset.cpus.exclusive.effective of a valid partition
> 2. cpuset.cpus.exclusive
> 3. cpuset.cpus
>
Hi, Longman,
This description is a bit confusing to me. cpuset.cpus.exclusive and
cpuset.cpus are user-settable
control files, while cpuset.cpus.exclusive.effective is a read-only file that
reflects the result of
applying cpuset.cpus.exclusive and cpuset.cpus after conflict resolution.
A partition can be established as long as cpuset.cpus.exclusive.effective is
not empty. I believe
cpuset.cpus.exclusive.effective represents the final effective CPU mask used
for the partition, so
it shouldn't be compared in priority with cpuset.cpus.exclusive or cpuset.cpus.
Rather, the latter
two are inputs that determine the former.
> So once a cpuset.cpus.exclusive is set without failure, it will
> always be allowed to form a valid partition as long as at least one
> CPU can be granted from its parent irrespective of the state of the
> siblings' cpuset.cpus values. Of course, setting cpuset.cpus.exclusive
> will fail if it conflicts with the cpuset.cpus.exclusive or the
> cpuset.cpus.exclusive.effective value of a sibling.
>
> Partition can still be created by setting only cpuset.cpus without
> setting cpuset.cpus.exclusive. However, any conflicting CPUs in sibling's
> cpuset.cpus.exclusive.effective and cpuset.cpus.exclusive values will
> be removed from its cpuset.cpus.exclusive.effective as long as there
> is still one or more CPUs left and can be granted from its parent. This
> CPU stripping is currently done in rm_siblings_excl_cpus().
>
> The new code will now try its best to enable the creation of new
> partitions with only cpuset.cpus set without invalidating existing ones.
> However it is not guaranteed that all the CPUs requested in cpuset.cpus
> will be used in the new partition even when all these CPUs can be
> granted from the parent.
>
> This is similar to the fact that cpuset.cpus.effective may not be
> able to include all the CPUs requested in cpuset.cpus. In this case,
> the parent may not able to grant all the exclusive CPUs requested in
> cpuset.cpus to cpuset.cpus.exclusive.effective if some of them have
> already been granted to other partitions earlier.
>
> With the creation of multiple sibling partitions by setting
> only cpuset.cpus, this does have the side effect that their exact
> cpuset.cpus.exclusive.effective settings will depend on the order of
> partition creation if there are conflicts. Due to the exclusive nature
> of the CPUs in a partition, it is not easy to make it fair other than
> the old behavior of invalidating all the conflicting partitions.
>
> For example,
> # echo "0-2" > A1/cpuset.cpus
> # echo "root" > A1/cpuset.cpus.partition
> # echo A1/cpuset.cpus.partition
> root
> # echo A1/cpuset.cpus.exclusive.effective
> 0-2
> # echo "2-4" > B1/cpuset.cpus
> # echo "root" > B1/cpuset.cpus.partition
> # echo B1/cpuset.cpus.partition
> root
> # echo B1/cpuset.cpus.exclusive.effective
> 3-4
> # echo B1/cpuset.cpus.effective
> 3-4
>
> For users who want to be sure that they can get most of the CPUs they
> want, cpuset.cpus.exclusive should be used instead if they can set
> it successfully without failure. Setting cpuset.cpus.exclusive will
> guarantee that sibling conflicts from then onward is no longer possible.
>
> To make this change, we have to separate out the is_cpu_exclusive()
> check in cpus_excl_conflict() into a cgroup v1 only
> cpuset1_cpus_excl_conflict() helper. The cpus_allowed_validate_change()
> helper is now no longer needed and can be removed.
>
> Some existing tests in test_cpuset_prs.sh are updated and new ones are
> added to reflect the new behavior. The cgroup-v2.rst doc file is also
> updated the clarify what exclusive CPUs will be used when a partition
> is created.
>
> Reported-by: Sun Shaojie <[email protected]>
> Closes:
> https://lore.kernel.org/lkml/[email protected]/
> Signed-off-by: Waiman Long <[email protected]>
> ---
> Documentation/admin-guide/cgroup-v2.rst | 32 +++++---
> kernel/cgroup/cpuset-internal.h | 3 +
> kernel/cgroup/cpuset-v1.c | 19 +++++
> kernel/cgroup/cpuset.c | 81 +++++++------------
> .../selftests/cgroup/test_cpuset_prs.sh | 26 ++++--
> 5 files changed, 90 insertions(+), 71 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst
> b/Documentation/admin-guide/cgroup-v2.rst
> index 510df2461aff..a3446db96cea 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -2584,9 +2584,9 @@ Cpuset Interface Files
> of this file will always be a subset of its parent's
> "cpuset.cpus.exclusive.effective" if its parent is not the root
> cgroup. It will also be a subset of "cpuset.cpus.exclusive"
> - if it is set. If "cpuset.cpus.exclusive" is not set, it is
> - treated to have an implicit value of "cpuset.cpus" in the
> - formation of local partition.
> + if it is set. This file should only be non-empty if either
> + "cpuset.cpus.exclusive" is set or when the current cpuset is
> + a valid partition root.
>
> cpuset.cpus.isolated
> A read-only and root cgroup only multiple values file.
> @@ -2618,13 +2618,22 @@ Cpuset Interface Files
> There are two types of partitions - local and remote. A local
> partition is one whose parent cgroup is also a valid partition
> root. A remote partition is one whose parent cgroup is not a
> - valid partition root itself. Writing to "cpuset.cpus.exclusive"
> - is optional for the creation of a local partition as its
> - "cpuset.cpus.exclusive" file will assume an implicit value that
> - is the same as "cpuset.cpus" if it is not set. Writing the
> - proper "cpuset.cpus.exclusive" values down the cgroup hierarchy
> - before the target partition root is mandatory for the creation
> - of a remote partition.
> + valid partition root itself.
> +
> + Writing to "cpuset.cpus.exclusive" is optional for the creation
> + of a local partition as its "cpuset.cpus.exclusive" file will
> + assume an implicit value that is the same as "cpuset.cpus" if it
> + is not set. Writing the proper "cpuset.cpus.exclusive" values
> + down the cgroup hierarchy before the target partition root is
> + mandatory for the creation of a remote partition.
> +
> + Not all the CPUs requested in "cpuset.cpus.exclusive" can be
> + used to form a new partition. Only those that were present
> + in its parent's "cpuset.cpus.exclusive.effective" control
> + file can be used. For partitions created without setting
> + "cpuset.cpus.exclusive", exclusive CPUs specified in sibling's
> + "cpuset.cpus.exclusive" or "cpuset.cpus.exclusive.effective"
> + also cannot be used.
>
> Currently, a remote partition cannot be created under a local
> partition. All the ancestors of a remote partition root except
> @@ -2632,6 +2641,9 @@ Cpuset Interface Files
>
> The root cgroup is always a partition root and its state cannot
> be changed. All other non-root cgroups start out as "member".
> + Even though the "cpuset.cpus.exclusive*" control files are not
> + present in the root cgroup, they are implicitly the same as
> + "cpuset.cpus".
>
> When set to "root", the current cgroup is the root of a new
> partition or scheduling domain. The set of exclusive CPUs is
> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
> index e718a4f54360..e8e2683cb067 100644
> --- a/kernel/cgroup/cpuset-internal.h
> +++ b/kernel/cgroup/cpuset-internal.h
> @@ -312,6 +312,7 @@ void cpuset1_hotplug_update_tasks(struct cpuset *cs,
> struct cpumask *new_cpus, nodemask_t *new_mems,
> bool cpus_updated, bool mems_updated);
> int cpuset1_validate_change(struct cpuset *cur, struct cpuset *trial);
> +bool cpuset1_cpus_excl_conflict(struct cpuset *cs1, struct cpuset *cs2);
> void cpuset1_init(struct cpuset *cs);
> void cpuset1_online_css(struct cgroup_subsys_state *css);
> int cpuset1_generate_sched_domains(cpumask_var_t **domains,
> @@ -326,6 +327,8 @@ static inline void cpuset1_hotplug_update_tasks(struct
> cpuset *cs,
> bool cpus_updated, bool mems_updated) {}
> static inline int cpuset1_validate_change(struct cpuset *cur,
> struct cpuset *trial) { return 0; }
> +static inline bool cpuset1_cpus_excl_conflict(struct cpuset *cs1,
> + struct cpuset *cs2) { return false; }
> static inline void cpuset1_init(struct cpuset *cs) {}
> static inline void cpuset1_online_css(struct cgroup_subsys_state *css) {}
> static inline int cpuset1_generate_sched_domains(cpumask_var_t **domains,
> diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
> index ecfea7800f0d..04124c38a774 100644
> --- a/kernel/cgroup/cpuset-v1.c
> +++ b/kernel/cgroup/cpuset-v1.c
> @@ -373,6 +373,25 @@ int cpuset1_validate_change(struct cpuset *cur, struct
> cpuset *trial)
> return ret;
> }
>
> +/*
> + * cpuset1_cpus_excl_conflict() - Check if two cpusets have exclusive CPU
> conflicts
> + * to legacy (v1)
> + * @cs1: first cpuset to check
> + * @cs2: second cpuset to check
> + *
> + * Returns: true if CPU exclusivity conflict exists, false otherwise
> + *
> + * If either cpuset is CPU exclusive, their allowed CPUs cannot intersect.
> + */
> +bool cpuset1_cpus_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
> +{
> + if (is_cpu_exclusive(cs1) || is_cpu_exclusive(cs2))
> + return cpumask_intersects(cs1->cpus_allowed,
> + cs2->cpus_allowed);
> +
> + return false;
> +}
> +
> #ifdef CONFIG_PROC_PID_CPUSET
> /*
> * proc_cpuset_show()
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 30e31fac4fe3..c091b63dd3c9 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -129,6 +129,18 @@ static bool force_sd_rebuild;
> * For simplicity, a local partition can be created under a local or remote
> * partition but a remote partition cannot have any partition root in its
> * ancestor chain except the cgroup root.
> + *
> + * A valid partition can be formed by setting either cpus_allowed or
> + * exclusive_cpus. If there are exclusive CPU conflicts, the conflicting
> + * CPUs will be assigned to the effective_xcpus of the partition according
> + * to the appearance of those CPUs in cpumasks (in descending order of
> + * priority).
> + * 1. effective_xcpus of a valid partition
> + * 2. exclusive_cpus
> + * 3. cpus_allowed
> + *
> + * exclusive_cpus should be used for setting up partition if the users want
> + * to get as many CPUs as possible.
> */
Ditto
> #define PRS_MEMBER 0
> #define PRS_ROOT 1
> @@ -616,27 +628,25 @@ static inline bool cpusets_are_exclusive(struct cpuset
> *cs1, struct cpuset *cs2)
> * Returns: true if CPU exclusivity conflict exists, false otherwise
> *
> * Conflict detection rules:
> - * 1. If either cpuset is CPU exclusive, they must be mutually exclusive
> - * 2. exclusive_cpus masks cannot intersect between cpusets
> - * 3. The allowed CPUs of a sibling cpuset cannot be a subset of the new
> exclusive CPUs
> + * o cgroup v1
> + * See cpuset1_cpus_excl_conflict()
> + * o cgroup v2
> + * - The exclusive_cpus values cannot overlap.
> + * - New exclusive_cpus cannot be a superset of a sibling's cpus_allowed.
> */
> static inline bool cpus_excl_conflict(struct cpuset *trial, struct cpuset
> *sibling,
> bool xcpus_changed)
> {
> - /* If either cpuset is exclusive, check if they are mutually exclusive
> */
> - if (is_cpu_exclusive(trial) || is_cpu_exclusive(sibling))
> - return !cpusets_are_exclusive(trial, sibling);
> -
> - /* Exclusive_cpus cannot intersect */
> - if (cpumask_intersects(trial->exclusive_cpus, sibling->exclusive_cpus))
> - return true;
> + if (!cpuset_v2())
> + return cpuset1_cpus_excl_conflict(trial, sibling);
>
> /* The cpus_allowed of a sibling cpuset cannot be a subset of the new
> exclusive_cpus */
> if (xcpus_changed && !cpumask_empty(sibling->cpus_allowed) &&
> cpumask_subset(sibling->cpus_allowed, trial->exclusive_cpus))
> return true;
>
> - return false;
> + /* Exclusive_cpus cannot intersect */
> + return cpumask_intersects(trial->exclusive_cpus,
> sibling->exclusive_cpus);
> }
>
> static inline bool mems_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
> @@ -2312,43 +2322,6 @@ static enum prs_errcode validate_partition(struct
> cpuset *cs, struct cpuset *tri
> return PERR_NONE;
> }
>
> -static int cpus_allowed_validate_change(struct cpuset *cs, struct cpuset
> *trialcs,
> - struct tmpmasks *tmp)
> -{
> - int retval;
> - struct cpuset *parent = parent_cs(cs);
> -
> - retval = validate_change(cs, trialcs);
> -
> - if ((retval == -EINVAL) && cpuset_v2()) {
> - struct cgroup_subsys_state *css;
> - struct cpuset *cp;
> -
> - /*
> - * The -EINVAL error code indicates that partition sibling
> - * CPU exclusivity rule has been violated. We still allow
> - * the cpumask change to proceed while invalidating the
> - * partition. However, any conflicting sibling partitions
> - * have to be marked as invalid too.
> - */
> - trialcs->prs_err = PERR_NOTEXCL;
> - rcu_read_lock();
> - cpuset_for_each_child(cp, css, parent) {
> - struct cpumask *xcpus = user_xcpus(trialcs);
> -
> - if (is_partition_valid(cp) &&
> - cpumask_intersects(xcpus, cp->effective_xcpus)) {
> - rcu_read_unlock();
> - update_parent_effective_cpumask(cp,
> partcmd_invalidate, NULL, tmp);
> - rcu_read_lock();
> - }
> - }
> - rcu_read_unlock();
> - retval = 0;
> - }
> - return retval;
> -}
> -
> /**
> * partition_cpus_change - Handle partition state changes due to CPU mask
> updates
> * @cs: The target cpuset being modified
> @@ -2408,15 +2381,15 @@ static int update_cpumask(struct cpuset *cs, struct
> cpuset *trialcs,
> if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
> return 0;
>
> - if (alloc_tmpmasks(&tmp))
> - return -ENOMEM;
> -
> compute_trialcs_excpus(trialcs, cs);
> trialcs->prs_err = PERR_NONE;
>
> - retval = cpus_allowed_validate_change(cs, trialcs, &tmp);
> + retval = validate_change(cs, trialcs);
> if (retval < 0)
> - goto out_free;
> + return retval;
> +
> + if (alloc_tmpmasks(&tmp))
> + return -ENOMEM;
>
> /*
> * Check all the descendants in update_cpumasks_hier() if
> @@ -2439,7 +2412,7 @@ static int update_cpumask(struct cpuset *cs, struct
> cpuset *trialcs,
> /* Update CS_SCHED_LOAD_BALANCE and/or sched_domains, if necessary */
> if (cs->partition_root_state)
> update_partition_sd_lb(cs, old_prs);
> -out_free:
> +
> free_tmpmasks(&tmp);
> return retval;
> }
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index a17256d9f88a..ff4540b0490e 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -269,7 +269,7 @@ TEST_MATRIX=(
> " C0-3:S+ C1-3:S+ C2-3 . X2-3 X3:P2 . . 0
> A1:0-2|A2:3|A3:3 A1:P0|A2:P2 3"
> " C0-3:S+ C1-3:S+ C2-3 . X2-3 X2-3 X2-3:P2 . 0
> A1:0-1|A2:1|A3:2-3 A1:P0|A3:P2 2-3"
> " C0-3:S+ C1-3:S+ C2-3 . X2-3 X2-3 X2-3:P2:C3 . 0
> A1:0-1|A2:1|A3:2-3 A1:P0|A3:P2 2-3"
> - " C0-3:S+ C1-3:S+ C2-3 C2-3 . . . P2 0
> A1:0-3|A2:1-3|A3:2-3|B1:2-3 A1:P0|A3:P0|B1:P-2"
> + " C0-3:S+ C1-3:S+ C2-3 C2-3 . . . P2 0
> A1:0-1|A2:1|A3:1|B1:2-3 A1:P0|A3:P0|B1:P2"
> " C0-3:S+ C1-3:S+ C2-3 C4-5 . . . P2 0 B1:4-5
> B1:P2 4-5"
> " C0-3:S+ C1-3:S+ C2-3 C4 X2-3 X2-3 X2-3:P2 P2 0
> A3:2-3|B1:4 A3:P2|B1:P2 2-4"
> " C0-3:S+ C1-3:S+ C2-3 C4 X2-3 X2-3 X2-3:P2:C1-3 P2 0
> A3:2-3|B1:4 A3:P2|B1:P2 2-4"
> @@ -318,7 +318,7 @@ TEST_MATRIX=(
> # Invalid to valid local partition direct transition tests
> " C1-3:S+:P2 X4:P2 . . . . . . 0
> A1:1-3|XA1:1-3|A2:1-3:XA2: A1:P2|A2:P-2 1-3"
> " C1-3:S+:P2 X4:P2 . . . X3:P2 . . 0
> A1:1-2|XA1:1-3|A2:3:XA2:3 A1:P2|A2:P2 1-3"
> - " C0-3:P2 . . C4-6 C0-4 . . . 0
> A1:0-4|B1:4-6 A1:P-2|B1:P0"
> + " C0-3:P2 . . C4-6 C0-4 . . . 0
> A1:0-4|B1:5-6 A1:P2|B1:P0"
> " C0-3:P2 . . C4-6 C0-4:C0-3 . . . 0
> A1:0-3|B1:4-6 A1:P2|B1:P0 0-3"
>
> # Local partition invalidation tests
> @@ -388,10 +388,10 @@ TEST_MATRIX=(
> " C0-1:S+ C1 . C2-3 . P2 . . 0
> A1:0-1|A2:1 A1:P0|A2:P-2"
> " C0-1:S+ C1:P2 . C2-3 P1 . . . 0
> A1:0|A2:1 A1:P1|A2:P2 0-1|1"
>
> - # A non-exclusive cpuset.cpus change will invalidate partition and its
> siblings
> - " C0-1:P1 . . C2-3 C0-2 . . . 0
> A1:0-2|B1:2-3 A1:P-1|B1:P0"
> - " C0-1:P1 . . P1:C2-3 C0-2 . . . 0
> A1:0-2|B1:2-3 A1:P-1|B1:P-1"
> - " C0-1 . . P1:C2-3 C0-2 . . . 0
> A1:0-2|B1:2-3 A1:P0|B1:P-1"
> + # A non-exclusive cpuset.cpus change will not invalidate its siblings
> partition.
> + " C0-1:P1 . . C2-3 C0-2 . . . 0
> A1:0-2|B1:3 A1:P1|B1:P0"
> + " C0-1:P1 . . P1:C2-3 C0-2 . . . 0
> A1:0-1|XA1:0-1|B1:2-3 A1:P1|B1:P1"
> + " C0-1 . . P1:C2-3 C0-2 . . . 0
> A1:0-1|B1:2-3 A1:P0|B1:P1"
>
> # cpuset.cpus can overlap with sibling cpuset.cpus.exclusive but not
> subsumed by it
> " C0-3 . . C4-5 X5 . . . 0
> A1:0-3|B1:4-5"
> @@ -417,6 +417,14 @@ TEST_MATRIX=(
> " CX1-4:S+ CX2-4:P2 . C5-6 . . . P1:C3-6 0
> A1:1|A2:2-4|B1:5-6 \
>
> A1:P0|A2:P2:B1:P-1 2-4"
>
> + # When multiple partitions with conflicting cpuset.cpus are created, the
> + # latter created ones will only get what are left of the available
> exclusive
> + # CPUs.
> + " C1-3:P1 . . . . . . C3-5:P1 0
> A1:1-3|B1:4-5:XB1:4-5 A1:P1|B1:P1"
> +
> + # cpuset.cpus can be set to a subset of sibling's cpuset.cpus.exclusive
> + " C1-3:X1-3 . . C4-5 . . . C1-2 0
> A1:1-3|B1:1-2"
> +
> # old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs
> Pstate ISOLCPUS
> # ------ ------ ------ ------ ------ ------ ------ ------ ---- -----
> ------ --------
> # Failure cases:
> @@ -427,7 +435,7 @@ TEST_MATRIX=(
> # Changes to cpuset.cpus.exclusive that violate exclusivity rule is
> rejected
> " C0-3 . . C4-5 X0-3 . . X3-5 1
> A1:0-3|B1:4-5"
>
> - # cpuset.cpus cannot be a subset of sibling cpuset.cpus.exclusive
> + # cpuset.cpus.exclusive cannot be set to a superset of sibling's
> cpuset.cpus
> " C0-3 . . C4-5 X3-5 . . . 1
> A1:0-3|B1:4-5"
> )
>
> @@ -477,6 +485,10 @@ REMOTE_TEST_MATRIX=(
> . . X1-2:P2 X4-5:P1 . X1-7:P2
> p1:3|c11:1-2|c12:4:c22:5-6 \
>
> p1:P0|p2:P1|c11:P2|c12:P1|c22:P2 \
> 1-2,4-6|1-2,5-6"
> + # c12 whose cpuset.cpus CPUs are all granted to c11 will become invalid
> partition
> + " C1-5:P1:S+ . C1-4:P1 C2-3 . . \
> + . . . P1 . . p1:5|c11:1-4|c12:5 \
> + p1:P1|c11:P1|c12:P-1"
> )
>
> #
--
Best regards,
Ridong
