linux-kernel - Re: [PATCH v1] cpuset: Avoid unnecessary partition invalidation

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Message-ID: <380567da-9079-4a4d-afae-42bde42d2a58@huaweicloud.com>
Date: Wed, 12 Nov 2025 11:33:21 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Sun Shaojie <sunshaojie@...inos.cn>, longman@...hat.com
Cc: tj@...nel.org, hannes@...xchg.org, mkoutny@...e.com, shuah@...nel.org,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v1] cpuset: Avoid unnecessary partition invalidation



On 2025/11/12 10:11, Sun Shaojie wrote:
Hello Shaojie,

> Currently, when a non-exclusive cpuset's "cpuset.cpus" overlaps with a
> partitioned sibling, the sibling's partition state becomes invalid.
> However, this invalidation is often unnecessary.
> 
> This can be observed in specific configuration sequences:
> 
> Case 1: Partition created first, then non-exclusive cpuset overlaps
>  #1> mkdir -p /sys/fs/cgroup/A1
>  #2> echo "0-1" > /sys/fs/cgroup/A1/cpuset.cpus
>  #3> echo "root" > /sys/fs/cgroup/A1/cpuset.cpus.partition
>  #4> mkdir -p /sys/fs/cgroup/B1
>  #5> echo "0-3" > /sys/fs/cgroup/B1/cpuset.cpus
>  // A1's partition becomes "root invalid" - this is unnecessary
> 
> Case 2: Non-exclusive cpuset exists first, then partition created
>  #1> mkdir -p /sys/fs/cgroup/B1
>  #2> echo "0-1" > /sys/fs/cgroup/B1/cpuset.cpus
>  #3> mkdir -p /sys/fs/cgroup/A1
>  #4> echo "0-1" > /sys/fs/cgroup/A1/cpuset.cpus
>  #5> echo "root" > /sys/fs/cgroup/A1/cpuset.cpus.partition
>  // A1's partition becomes "root invalid" - this is unnecessary
> 
> In Case 1, the effective CPU mask of B1 can differ from its requested
> mask. B1 can use CPUs 2-3 which don't overlap with A1's exclusive
> CPUs (0-1), thus not violating A1's exclusivity requirement.
> 
> In Case 2, B1 can inherit the effective CPUs from its parent, so there
> is no need to invalidate A1's partition state.
> 
> This patch relaxes the overlap check to only consider conflicts between
> partitioned siblings, not between a partitioned cpuset and a regular
> non-exclusive one.
> 

Does this rule have any negative impact on your products?

The CPUs specified by the user (including cpuset.cpus and cpuset.cpus.exclusive) can be treated as
the dedicated exclusive CPUs for the partition. For the cases you provided, both siblings can be
partitions. For example, in case 1, A1 can also be converted to a partition. If this rule is
relaxed, I don’t see any check for exclusive conflicts when A1 becomes a partition.

Additionally, I think we should preserve the CPU affinity as the user intends as much as possible.

> Signed-off-by: Sun Shaojie <sunshaojie@...inos.cn>
> ---
>  kernel/cgroup/cpuset.c                            |  8 ++++----
>  tools/testing/selftests/cgroup/test_cpuset_prs.sh | 10 +++++-----
>  2 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 52468d2c178a..e0d27c9a101a 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -586,14 +586,14 @@ 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
> + * 1. If both cpusets are exclusive, they must be mutually exclusive
>   * 2. exclusive_cpus masks cannot intersect between cpusets
>   * 3. The allowed CPUs of one cpuset cannot be a subset of another's exclusive CPUs
>   */
>  static inline bool cpus_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
>  {
> -	/* If either cpuset is exclusive, check if they are mutually exclusive */
> -	if (is_cpu_exclusive(cs1) || is_cpu_exclusive(cs2))
> +	/* If both cpusets are exclusive, check if they are mutually exclusive */
> +	if (is_cpu_exclusive(cs1) && is_cpu_exclusive(cs2))
>  		return !cpusets_are_exclusive(cs1, cs2);
>  
>  	/* Exclusive_cpus cannot intersect */
> @@ -695,7 +695,7 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)
>  		goto out;
>  
>  	/*
> -	 * If either I or some sibling (!= me) is exclusive, we can't
> +	 * If both I and some sibling (!= me) are exclusive, we can't
>  	 * overlap. exclusive_cpus cannot overlap with each other if set.
>  	 */
>  	ret = -EINVAL;
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index a17256d9f88a..903dddfe88d7 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 2-3"
>  	" 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 0-4"
>  	"  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"
> +	# A non-exclusive cpuset.cpus change will not invalidate partition and its siblings
> +	"  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 A1:0-2|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"
> +	"   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"

-- 
Best regards,
Ridong