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Subject[PATCH 16/31] workqueue: introduce workqueue_attrs
Date
Introduce struct workqueue_attrs which carries worker attributes -
currently the nice level and allowed cpumask along with helper
routines alloc_workqueue_attrs() and free_workqueue_attrs().

Each worker_pool now carries ->attrs describing the attributes of its
workers. All functions dealing with cpumask and nice level of workers
are updated to follow worker_pool->attrs instead of determining them
from other characteristics of the worker_pool, and init_workqueues()
is updated to set worker_pool->attrs appropriately for all standard
pools.

Note that create_worker() is updated to always perform set_user_nice()
and use set_cpus_allowed_ptr() combined with manual assertion of
PF_THREAD_BOUND instead of kthread_bind(). This simplifies handling
random attributes without affecting the outcome.

This patch doesn't introduce any behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/workqueue.h | 12 ++++++
kernel/workqueue.c | 103 ++++++++++++++++++++++++++++++++++++----------
2 files changed, 93 insertions(+), 22 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 899be66..2683e8e 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -115,6 +115,15 @@ struct delayed_work {
int cpu;
};

+/*
+ * A struct for workqueue attributes. This can be used to change
+ * attributes of an unbound workqueue.
+ */
+struct workqueue_attrs {
+ int nice; /* nice level */
+ cpumask_var_t cpumask; /* allowed CPUs */
+};
+
static inline struct delayed_work *to_delayed_work(struct work_struct *work)
{
return container_of(work, struct delayed_work, work);
@@ -399,6 +408,9 @@ __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,

extern void destroy_workqueue(struct workqueue_struct *wq);

+struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask);
+void free_workqueue_attrs(struct workqueue_attrs *attrs);
+
extern bool queue_work_on(int cpu, struct workqueue_struct *wq,
struct work_struct *work);
extern bool queue_work(struct workqueue_struct *wq, struct work_struct *work);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f97539b..7eba824 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -148,6 +148,8 @@ struct worker_pool {
struct mutex assoc_mutex; /* protect POOL_DISASSOCIATED */
struct ida worker_ida; /* L: for worker IDs */

+ struct workqueue_attrs *attrs; /* I: worker attributes */
+
/*
* The current concurrency level. As it's likely to be accessed
* from other CPUs during try_to_wake_up(), put it in a separate
@@ -1563,14 +1565,13 @@ __acquires(&pool->lock)
* against POOL_DISASSOCIATED.
*/
if (!(pool->flags & POOL_DISASSOCIATED))
- set_cpus_allowed_ptr(current, get_cpu_mask(pool->cpu));
+ set_cpus_allowed_ptr(current, pool->attrs->cpumask);

spin_lock_irq(&pool->lock);
if (pool->flags & POOL_DISASSOCIATED)
return false;
if (task_cpu(current) == pool->cpu &&
- cpumask_equal(&current->cpus_allowed,
- get_cpu_mask(pool->cpu)))
+ cpumask_equal(&current->cpus_allowed, pool->attrs->cpumask))
return true;
spin_unlock_irq(&pool->lock);

@@ -1677,7 +1678,7 @@ static void rebind_workers(struct worker_pool *pool)
* wq doesn't really matter but let's keep @worker->pool
* and @pwq->pool consistent for sanity.
*/
- if (std_worker_pool_pri(worker->pool))
+ if (worker->pool->attrs->nice < 0)
wq = system_highpri_wq;
else
wq = system_wq;
@@ -1719,7 +1720,7 @@ static struct worker *alloc_worker(void)
*/
static struct worker *create_worker(struct worker_pool *pool)
{
- const char *pri = std_worker_pool_pri(pool) ? "H" : "";
+ const char *pri = pool->attrs->nice < 0 ? "H" : "";
struct worker *worker = NULL;
int id = -1;

@@ -1749,24 +1750,23 @@ static struct worker *create_worker(struct worker_pool *pool)
if (IS_ERR(worker->task))
goto fail;

- if (std_worker_pool_pri(pool))
- set_user_nice(worker->task, HIGHPRI_NICE_LEVEL);
+ set_user_nice(worker->task, pool->attrs->nice);
+ set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);

/*
- * Determine CPU binding of the new worker depending on
- * %POOL_DISASSOCIATED. The caller is responsible for ensuring the
- * flag remains stable across this function. See the comments
- * above the flag definition for details.
- *
- * As an unbound worker may later become a regular one if CPU comes
- * online, make sure every worker has %PF_THREAD_BOUND set.
+ * %PF_THREAD_BOUND is used to prevent userland from meddling with
+ * cpumask of workqueue workers. This is an abuse. We need
+ * %PF_KERNEL_CPUMASK.
*/
- if (!(pool->flags & POOL_DISASSOCIATED)) {
- kthread_bind(worker->task, pool->cpu);
- } else {
- worker->task->flags |= PF_THREAD_BOUND;
+ worker->task->flags |= PF_THREAD_BOUND;
+
+ /*
+ * The caller is responsible for ensuring %POOL_DISASSOCIATED
+ * remains stable across this function. See the comments above the
+ * flag definition for details.
+ */
+ if (pool->flags & POOL_DISASSOCIATED)
worker->flags |= WORKER_UNBOUND;
- }

return worker;
fail:
@@ -3121,7 +3121,52 @@ int keventd_up(void)
return system_wq != NULL;
}

-static void init_worker_pool(struct worker_pool *pool)
+/**
+ * free_workqueue_attrs - free a workqueue_attrs
+ * @attrs: workqueue_attrs to free
+ *
+ * Undo alloc_workqueue_attrs().
+ */
+void free_workqueue_attrs(struct workqueue_attrs *attrs)
+{
+ if (attrs) {
+ free_cpumask_var(attrs->cpumask);
+ kfree(attrs);
+ }
+}
+
+/**
+ * alloc_workqueue_attrs - allocate a workqueue_attrs
+ * @gfp_mask: allocation mask to use
+ *
+ * Allocate a new workqueue_attrs, initialize with default settings and
+ * return it. Returns NULL on failure.
+ */
+struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask)
+{
+ struct workqueue_attrs *attrs;
+
+ attrs = kzalloc(sizeof(*attrs), gfp_mask);
+ if (!attrs)
+ goto fail;
+ if (!alloc_cpumask_var(&attrs->cpumask, gfp_mask))
+ goto fail;
+
+ cpumask_setall(attrs->cpumask);
+ return attrs;
+fail:
+ free_workqueue_attrs(attrs);
+ return NULL;
+}
+
+/**
+ * init_worker_pool - initialize a newly zalloc'd worker_pool
+ * @pool: worker_pool to initialize
+ *
+ * Initiailize a newly zalloc'd @pool. It also allocates @pool->attrs.
+ * Returns 0 on success, -errno on failure.
+ */
+static int init_worker_pool(struct worker_pool *pool)
{
spin_lock_init(&pool->lock);
pool->flags |= POOL_DISASSOCIATED;
@@ -3139,6 +3184,11 @@ static void init_worker_pool(struct worker_pool *pool)
mutex_init(&pool->manager_mutex);
mutex_init(&pool->assoc_mutex);
ida_init(&pool->worker_ida);
+
+ pool->attrs = alloc_workqueue_attrs(GFP_KERNEL);
+ if (!pool->attrs)
+ return -ENOMEM;
+ return 0;
}

static int alloc_and_link_pwqs(struct workqueue_struct *wq)
@@ -3791,7 +3841,8 @@ out_unlock:

static int __init init_workqueues(void)
{
- int cpu;
+ int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
+ int i, cpu;

/* make sure we have enough bits for OFFQ pool ID */
BUILD_BUG_ON((1LU << (BITS_PER_LONG - WORK_OFFQ_POOL_SHIFT)) <
@@ -3808,10 +3859,18 @@ static int __init init_workqueues(void)
for_each_wq_cpu(cpu) {
struct worker_pool *pool;

+ i = 0;
for_each_std_worker_pool(pool, cpu) {
- init_worker_pool(pool);
+ BUG_ON(init_worker_pool(pool));
pool->cpu = cpu;

+ if (cpu != WORK_CPU_UNBOUND)
+ cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
+ else
+ cpumask_setall(pool->attrs->cpumask);
+
+ pool->attrs->nice = std_nice[i++];
+
/* alloc pool ID */
BUG_ON(worker_pool_assign_id(pool));
}
--
1.8.1.2


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