[RFC PATCH v3 1/3] sched/isolation: Add infrastructure for dynamic CPU isolation

Costa Shulyupin
2024-10-29T12:08:19Z

Introduce the infrastructure function housekeeping_update()
to modify housekeeping_cpumask at runtime and update the
configurations of dependent subsystems accordingly in
following patches.

Parent patch:
sched/isolation: Exclude dynamically isolated CPUs from housekeeping masks
https://lore.kernel.org/lkml/20240821142312.236970-1-longman@redhat.com/

Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>

---

Note: In theory, updating housekeeping.flags only once is possible.
However, this approach would make this and following code less clear
and harder to follow and review.

Changes in v3:
- Remove redundant WRITE_ONCE. The first WRITE_ONCE is located
in housekeeping_update() because this function will
update dependent subsystems with changes of the housekeeping masks.

Changes in v2:
- remove unnecessary `err` variable
- add for_each_clear_bit... to clear isolated CPUs
- Address Gleixner's comments:
- use WRITE_ONCE to change housekeeping.flags
- use `struct cpumask *update` in signature of housekeeping_update

v1:
- https://lore.kernel.org/lkml/20240516190437.3545310-2-costa.shul@redhat.com/
---
kernel/sched/isolation.c | 43 ++++++++++++++++++++++++++++++++++++----
1 file changed, 39 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 2ee47bc25aea..ebbb215505e8 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -127,6 +127,40 @@ static void __init housekeeping_setup_type(enum hk_type type,
housekeeping_staging);
}

+/*
+ * housekeeping_update - change housekeeping.cpumasks[type] and propagate the
+ * change.
+ */
+static int housekeeping_update(enum hk_type type, const struct cpumask *update)
+{
+ struct {
+ struct cpumask changed;
+ struct cpumask enable;
+ struct cpumask disable;
+ } *masks;
+
+ masks = kmalloc(sizeof(*masks), GFP_KERNEL);
+ if (!masks)
+ return -ENOMEM;
+
+ lockdep_assert_cpus_held();
+ cpumask_xor(&masks->changed, housekeeping_cpumask(type), update);
+ cpumask_and(&masks->enable, &masks->changed, update);
+ cpumask_andnot(&masks->disable, &masks->changed, update);
+ cpumask_copy(housekeeping.cpumasks[type], update);
+ WRITE_ONCE(housekeeping.flags, housekeeping.flags | BIT(type));
+ if (!static_branch_unlikely(&housekeeping_overridden))
+ static_key_enable_cpuslocked(&housekeeping_overridden.key);
+
+ /* Add here code to update dependent subsystems with
+ * changes of the housekeeping masks.
+ */
+
+ kfree(masks);
+
+ return 0;
+}
+
static int __init housekeeping_setup(char *str, unsigned long flags)
{
cpumask_var_t non_housekeeping_mask, housekeeping_staging;
@@ -330,10 +364,12 @@ int housekeeping_exlude_isolcpus(const struct cpumask *isolcpus, unsigned long f
/*
* Reset housekeeping to bootup default
*/
+
+ for_each_clear_bit(type, &boot_hk_flags, HK_TYPE_MAX)
+ housekeeping_update(type, cpu_possible_mask);
for_each_set_bit(type, &boot_hk_flags, HK_TYPE_MAX)
- cpumask_copy(housekeeping.cpumasks[type], boot_hk_cpumask);
+ housekeeping_update(type, boot_hk_cpumask);

- WRITE_ONCE(housekeeping.flags, boot_hk_flags);
if (!boot_hk_flags && static_key_enabled(&housekeeping_overridden))
static_key_disable_cpuslocked(&housekeeping_overridden.key);
return 0;
@@ -358,9 +394,8 @@ int housekeeping_exlude_isolcpus(const struct cpumask *isolcpus, unsigned long f
cpumask_andnot(tmp_mask, src_mask, isolcpus);
if (!cpumask_intersects(tmp_mask, cpu_online_mask))
return -EINVAL; /* Invalid isolated CPUs */
- cpumask_copy(housekeeping.cpumasks[type], tmp_mask);
+ housekeeping_update(type, tmp_mask);
}
- WRITE_ONCE(housekeeping.flags, boot_hk_flags | flags);
excluded = true;
if (!static_key_enabled(&housekeeping_overridden))
static_key_enable_cpuslocked(&housekeeping_overridden.key);
--
2.47.0