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Message-ID: <19fa5a93-4cc9-4f84-891c-b3b096a68799@huaweicloud.com>
Date: Fri, 14 Nov 2025 08:50:07 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Sun Shaojie <sunshaojie@...inos.cn>, llong@...hat.com
Cc: cgroups@...r.kernel.org, hannes@...xchg.org,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
mkoutny@...e.com, shuah@...nel.org, tj@...nel.org
Subject: Re: [PATCH v2] cpuset: relax the overlap check for cgroup-v2
On 2025/11/13 21:14, Sun Shaojie wrote:
> In cgroup v2, a mutual overlap check is required when at least one of two
> cpusets is exclusive. However, this check should be relaxed and limited to
> cases where both cpusets are exclusive.
>
> The table 1 shows the partition states of A1 and B1 after each step before
> applying this patch.
>
> Table 1: Before applying the patch
> Step | A1's prstate | B1's prstate |
> #1> mkdir -p A1 | member | |
> #2> echo "0-1" > A1/cpuset.cpus | member | |
> #3> echo "root" > A1/cpuset.cpus.partition | root | |
> #4> mkdir -p B1 | root | member |
> #5> echo "0-3" > B1/cpuset.cpus | root invalid | member |
> #6> echo "root" > B1/cpuset.cpus.partition | root invalid | root invalid |
>
> After step #5, A1 changes from "root" to "root invalid" because its CPUs
> (0-1) overlap with those requested by B1 (0-3). However, B1 can actually
> use CPUs 2-3, so it would be more reasonable for A1 to remain as "root."
>
> This patch relaxes the exclusive cpuset check for cgroup v2 while
> preserving the current cgroup v1 behavior.
>
> Signed-off-by: Sun Shaojie <sunshaojie@...inos.cn>
>
> ---
> v1 -> v2:
> - Keeps the current cgroup v1 behavior unchanged
> - Link: https://lore.kernel.org/cgroups/c8e234f4-2c27-4753-8f39-8ae83197efd3@redhat.com
> ---
> kernel/cgroup/cpuset.c | 9 +++++++--
> tools/testing/selftests/cgroup/test_cpuset_prs.sh | 10 +++++-----
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 52468d2c178a..3240b3ab5998 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -592,8 +592,13 @@ static inline bool cpusets_are_exclusive(struct cpuset *cs1, struct cpuset *cs2)
> */
> 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);
> +
> + /* In cgroup-v1, if either cpuset is exclusive, check if they are mutually exclusive */
> + if (!is_in_v2_mode() &&
> + (is_cpu_exclusive(cs1) != is_cpu_exclusive(cs2)))
> return !cpusets_are_exclusive(cs1, cs2);
>
I prefer adding a helper function in the cpuset-v1.c file, similar to cpus_excl_conflict_legacy().
For cpuset v1, it can simply return cpus_excl_conflict_legacy(). It seems that other rules are not
relevant to v1.
> /* Exclusive_cpus cannot intersect */
> 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
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