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@kylinos.cn
--- v1 -> v2: - Keeps the current cgroup v1 behavior unchanged - Link: https://lore.kernel.org/cgroups/c8e234f4-2c27-4753-8f39-8ae83197efd3@redhat.... --- 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);
/* 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"
On 11/13/25 8:14 AM, 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@kylinos.cn
v1 -> v2:
- Keeps the current cgroup v1 behavior unchanged
- Link: https://lore.kernel.org/cgroups/c8e234f4-2c27-4753-8f39-8ae83197efd3@redhat....
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() &&
You should just use cpuset_v2() here as is_in_v2_mode() checks an additional v1 specific mode that is irrelevant wrt to exclusive bit handling. Also please update the functional comment about difference in v1 vs. v2 behavior.
Note that we may have to update other conflict checking code in cpuset.c to make this new behavior more consistent.
Thanks, Longman
(is_cpu_exclusive(cs1) != is_cpu_exclusive(cs2)))/* 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"
Hello.
On Thu, Nov 13, 2025 at 09:14:34PM +0800, Sun Shaojie sunshaojie@kylinos.cn 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."
I remember there was the addition of cgroup_file_notify() for the cpuset.cpus.partition so that such changes can be watched for.
I may not be seeing whole picture, so I ask -- why would it be "more reasonable" for A1 to remain root. From this description it looks like you'd silently convert B1's effective cpus to 2-3 but IIUC the code change that won't happen but you'd reject the write of "0-3" instead.
Isn't here missing Table 2: After applying the patch? I'm asking because of the number 1 but also because it'd make the intention clearer ;-), perhaps with a column for cpuset.cpus.effective.
Thanks, Michal
On 2025/11/14 1:07, Michal Koutný wrote:
Hello.
On Thu, Nov 13, 2025 at 09:14:34PM +0800, Sun Shaojie sunshaojie@kylinos.cn 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."
I remember there was the addition of cgroup_file_notify() for the cpuset.cpus.partition so that such changes can be watched for.
This behavior is visible to user space, I think.
After further consideration, I still suggest retaining this rule.
If we relax this rule, the following checks should also be relaxed?
/* The cpus_allowed of one cpuset cannot be a subset of another cpuset's exclusive_cpus */ if (!cpumask_empty(cs1->cpus_allowed) && cpumask_subset(cs1->cpus_allowed, cs2->exclusive_cpus)) return true;
if (!cpumask_empty(cs2->cpus_allowed) && cpumask_subset(cs2->cpus_allowed, cs1->exclusive_cpus)) return true;
For am example: Step | A1's prstate | B1's prstate | #1> mkdir -p A1 | member | | #2> echo "0-1" > A1/cpuset.cpus.exclusive | member | | #3> echo "root" > A1/cpuset.cpus.partition | root | | #4> mkdir -p B1 | root | member | #5> echo "0" > B1/cpuset.cpus | root invalid | member |
Currently, we mark A1 as invalid. But similar to the logic in this patch, why must A1 be invalidated? B1 could also use the parent's effective CPUs, right?
This raises the question: Should we relax the restriction to allow a cpuset's cpus to be a subset of its siblings' exclusive_cpus, thereby keeping A1 valid? If we do this, users may struggle to understand what their cpuset.cpus.effective value is (and why it has that value)—contrary to their expectations.
I may not be seeing whole picture, so I ask -- why would it be "more reasonable" for A1 to remain root. From this description it looks like you'd silently convert B1's effective cpus to 2-3 but IIUC the code change that won't happen but you'd reject the write of "0-3" instead.
Isn't here missing Table 2: After applying the patch? I'm asking because of the number 1 but also because it'd make the intention clearer ;-), perhaps with a column for cpuset.cpus.effective.
Thanks, Michal
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@kylinos.cn
v1 -> v2:
- Keeps the current cgroup v1 behavior unchanged
- Link: https://lore.kernel.org/cgroups/c8e234f4-2c27-4753-8f39-8ae83197efd3@redhat....
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)))
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"
On 2025/11/13 22:57, Waiman Long wrote:
On 11/13/25 8:14 AM, Sun Shaojie wrote:
... 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() &&
You should just use cpuset_v2() here as is_in_v2_mode() checks an additional v1 specific mode that is irrelevant wrt to exclusive bit handling. Also please update the functional comment about difference in v1 vs. v2 behavior.
Note that we may have to update other conflict checking code in cpuset.c to make this new behavior more consistent.
Thanks, Longman
(is_cpu_exclusive(cs1) != is_cpu_exclusive(cs2)))/* Exclusive_cpus cannot intersect */
Thank you for the correction.I will update the patch accordingly.
Tnanks, Sun Shaojie
Hi, Michal
On 2025/11/14 01:07, Michal Koutný wrote:
On Thu, Nov 13, 2025 at 09:14:34PM +0800, Sun Shaojie sunshaojie@kylinos.cn 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."
I remember there was the addition of cgroup_file_notify() for the cpuset.cpus.partition so that such changes can be watched for.
I may not be seeing whole picture, so I ask -- why would it be "more reasonable" for A1 to remain root. From this description it looks like you'd silently convert B1's effective cpus to 2-3 but IIUC the code change that won't happen but you'd reject the write of "0-3" instead.
The desired outcome is that after step #5, although B1 writes "0-3" to cpuset.cpus, A1 can still remain as "root", and B1 ends up with effective CPUs of 2-3. In summary, We want to avoid A1's invalidation when B1 changes its cpuset.cpus. Because cgroup v2 allows the effective CPU mask of a cpuset to differ from its requested mask.
Indeed, this issue was discussed in detail during the v1 review. https://lore.kernel.org/cgroups/c8e234f4-2c27-4753-8f39-8ae83197efd3@redhat....
Isn't here missing Table 2: After applying the patch? I'm asking because of the number 1 but also because it'd make the intention clearer ;-), perhaps with a column for cpuset.cpus.effective.
Thanks for the suggestion. I will update the patch description accordingly.
Thanks, Sun Shaojie
On 2025/11/14 08:50, Chen Ridong Wrote:
On 2025/11/13 21:14, Sun Shaojie wrote:
... 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)))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 */
Hi, Ridong,
Thank you for the suggestion.I will update the patch accordingly.
Thanks, Sunshaojie
On 2025/11/14 14:33, Sun Shaojie wrote:
On 2025/11/14 08:50, Chen Ridong Wrote:
On 2025/11/13 21:14, Sun Shaojie wrote:
... 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)))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 */
Hi, Ridong,
Thank you for the suggestion.I will update the patch accordingly.
If we are ready to relax this rule, adding the v1 logic in cpuset1_validate_change might be appropriate. However, as I mentioned in my reply to Michal, I believe further discussion is needed.
linux-kselftest-mirror@lists.linaro.org
-
Chen Ridong -
Michal Koutný -
Sun Shaojie -
Waiman Long