Currently if a user enqueue a work item using schedule_delayed_work() the used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to schedule_work() that is using system_wq and queue_work(), that makes use again of WORK_CPU_UNBOUND. This lack of consistentcy cannot be addressed without refactoring the API. system_wq is a per-CPU worqueue, yet nothing in its name tells about that CPU affinity constraint, which is very often not required by users. Make it clear by adding a system_percpu_wq. queue_work() / queue_delayed_work() mod_delayed_work() will now use the new per-cpu wq: whether the user still stick on the old name a warn will be printed along a wq redirect to the new one. This patch add the new system_percpu_wq except for mm, fs and net subsystem, whom are handled in separated patches. The old wq will be kept for a few release cylces. Suggested-by: Tejun Heo Signed-off-by: Marco Crivellari --- kernel/bpf/cgroup.c | 2 +- kernel/bpf/cpumap.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index 84f58f3d028a..b8699ec4d766 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -27,7 +27,7 @@ EXPORT_SYMBOL(cgroup_bpf_enabled_key); /* * cgroup bpf destruction makes heavy use of work items and there can be a lot * of concurrent destructions. Use a separate workqueue so that cgroup bpf - * destruction work items don't end up filling up max_active of system_wq + * destruction work items don't end up filling up max_active of system_percpu_wq * which may lead to deadlock. */ static struct workqueue_struct *cgroup_bpf_destroy_wq; diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c index 67e8a2fc1a99..1ab8e6876618 100644 --- a/kernel/bpf/cpumap.c +++ b/kernel/bpf/cpumap.c @@ -551,7 +551,7 @@ static void __cpu_map_entry_replace(struct bpf_cpu_map *cmap, old_rcpu = unrcu_pointer(xchg(&cmap->cpu_map[key_cpu], RCU_INITIALIZER(rcpu))); if (old_rcpu) { INIT_RCU_WORK(&old_rcpu->free_work, __cpu_map_entry_free); - queue_rcu_work(system_wq, &old_rcpu->free_work); + queue_rcu_work(system_percpu_wq, &old_rcpu->free_work); } } -- 2.51.0 Currently if a user enqueue a work item using schedule_delayed_work() the used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to schedule_work() that is using system_wq and queue_work(), that makes use again of WORK_CPU_UNBOUND. This lack of consistentcy cannot be addressed without refactoring the API. system_unbound_wq should be the default workqueue so as not to enforce locality constraints for random work whenever it's not required. Adding system_dfl_wq to encourage its use when unbound work should be used. queue_work() / queue_delayed_work() / mod_delayed_work() will now use the new unbound wq: whether the user still use the old wq a warn will be printed along with a wq redirect to the new one. The old system_unbound_wq will be kept for a few release cycles. Suggested-by: Tejun Heo Signed-off-by: Marco Crivellari --- kernel/bpf/helpers.c | 4 ++-- kernel/bpf/memalloc.c | 2 +- kernel/bpf/syscall.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index e3a2662f4e33..b969ca4d7af0 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1593,7 +1593,7 @@ void bpf_timer_cancel_and_free(void *val) * timer callback. */ if (this_cpu_read(hrtimer_running)) { - queue_work(system_unbound_wq, &t->cb.delete_work); + queue_work(system_dfl_wq, &t->cb.delete_work); return; } @@ -1606,7 +1606,7 @@ void bpf_timer_cancel_and_free(void *val) if (hrtimer_try_to_cancel(&t->timer) >= 0) kfree_rcu(t, cb.rcu); else - queue_work(system_unbound_wq, &t->cb.delete_work); + queue_work(system_dfl_wq, &t->cb.delete_work); } else { bpf_timer_delete_work(&t->cb.delete_work); } diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index 889374722d0a..bd45dda9dc35 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -736,7 +736,7 @@ static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress) /* Defer barriers into worker to let the rest of map memory to be freed */ memset(ma, 0, sizeof(*ma)); INIT_WORK(©->work, free_mem_alloc_deferred); - queue_work(system_unbound_wq, ©->work); + queue_work(system_dfl_wq, ©->work); } void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 9794446bc8c6..bb6f85fda240 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -901,7 +901,7 @@ static void bpf_map_free_in_work(struct bpf_map *map) /* Avoid spawning kworkers, since they all might contend * for the same mutex like slab_mutex. */ - queue_work(system_unbound_wq, &map->work); + queue_work(system_dfl_wq, &map->work); } static void bpf_map_free_rcu_gp(struct rcu_head *rcu) -- 2.51.0 Currently if a user enqueue a work item using schedule_delayed_work() the used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to schedule_work() that is using system_wq and queue_work(), that makes use again of WORK_CPU_UNBOUND. This lack of consistentcy cannot be addressed without refactoring the API. alloc_workqueue() treats all queues as per-CPU by default, while unbound workqueues must opt-in via WQ_UNBOUND. This default is suboptimal: most workloads benefit from unbound queues, allowing the scheduler to place worker threads where they’re needed and reducing noise when CPUs are isolated. This default is suboptimal: most workloads benefit from unbound queues, allowing the scheduler to place worker threads where they’re needed and reducing noise when CPUs are isolated. This patch adds a new WQ_PERCPU flag to explicitly request the use of the per-CPU behavior. Both flags coexist for one release cycle to allow callers to transition their calls. Once migration is complete, WQ_UNBOUND can be removed and unbound will become the implicit default. With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND), any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND must now use WQ_PERCPU. All existing users have been updated accordingly. Suggested-by: Tejun Heo Signed-off-by: Marco Crivellari --- kernel/bpf/cgroup.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index b8699ec4d766..f3da9400c178 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -34,7 +34,8 @@ static struct workqueue_struct *cgroup_bpf_destroy_wq; static int __init cgroup_bpf_wq_init(void) { - cgroup_bpf_destroy_wq = alloc_workqueue("cgroup_bpf_destroy", 0, 1); + cgroup_bpf_destroy_wq = alloc_workqueue("cgroup_bpf_destroy", + WQ_PERCPU, 1); if (!cgroup_bpf_destroy_wq) panic("Failed to alloc workqueue for cgroup bpf destroy.\n"); return 0; -- 2.51.0