diff options
Diffstat (limited to 'include/linux/workqueue.h')
| -rw-r--r-- | include/linux/workqueue.h | 35 |
1 files changed, 32 insertions, 3 deletions
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index 78047d0d9882..232baea90a1d 100644 --- a/include/linux/workqueue.h +++ b/include/linux/workqueue.h @@ -398,6 +398,13 @@ enum wq_consts { WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */ WQ_UNBOUND_MAX_ACTIVE = WQ_MAX_ACTIVE, WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2, + + /* + * Per-node default cap on min_active. Unless explicitly set, min_active + * is set to min(max_active, WQ_DFL_MIN_ACTIVE). For more details, see + * workqueue_struct->min_active definition. + */ + WQ_DFL_MIN_ACTIVE = 8, }; /* @@ -440,11 +447,33 @@ extern struct workqueue_struct *system_freezable_power_efficient_wq; * alloc_workqueue - allocate a workqueue * @fmt: printf format for the name of the workqueue * @flags: WQ_* flags - * @max_active: max in-flight work items per CPU, 0 for default + * @max_active: max in-flight work items, 0 for default * remaining args: args for @fmt * - * Allocate a workqueue with the specified parameters. For detailed - * information on WQ_* flags, please refer to + * For a per-cpu workqueue, @max_active limits the number of in-flight work + * items for each CPU. e.g. @max_active of 1 indicates that each CPU can be + * executing at most one work item for the workqueue. + * + * For unbound workqueues, @max_active limits the number of in-flight work items + * for the whole system. e.g. @max_active of 16 indicates that that there can be + * at most 16 work items executing for the workqueue in the whole system. + * + * As sharing the same active counter for an unbound workqueue across multiple + * NUMA nodes can be expensive, @max_active is distributed to each NUMA node + * according to the proportion of the number of online CPUs and enforced + * independently. + * + * Depending on online CPU distribution, a node may end up with per-node + * max_active which is significantly lower than @max_active, which can lead to + * deadlocks if the per-node concurrency limit is lower than the maximum number + * of interdependent work items for the workqueue. + * + * To guarantee forward progress regardless of online CPU distribution, the + * concurrency limit on every node is guaranteed to be equal to or greater than + * min_active which is set to min(@max_active, %WQ_DFL_MIN_ACTIVE). This means + * that the sum of per-node max_active's may be larger than @max_active. + * + * For detailed information on %WQ_* flags, please refer to * Documentation/core-api/workqueue.rst. * * RETURNS: |