diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst index 56af317508c9ce..c73a6df6a11877 100644 --- a/Documentation/core-api/workqueue.rst +++ b/Documentation/core-api/workqueue.rst @@ -353,9 +353,10 @@ Affinity Scopes An unbound workqueue groups CPUs according to its affinity scope to improve cache locality. For example, if a workqueue is using the default affinity scope of "cache", it will group CPUs according to last level cache -boundaries. A work item queued on the workqueue will be processed by a -worker running on one of the CPUs which share the last level cache with the -issuing CPU. +boundaries. A work item queued on the workqueue will be assigned to a worker +on one of the CPUs which share the last level cache with the issuing CPU. +Once started, the worker may or may not be allowed to move outside the scope +depending on the ``affinity_strict`` setting of the scope. Workqueue currently supports the following five affinity scopes. @@ -391,6 +392,21 @@ directory. ``affinity_scope`` Read to see the current affinity scope. Write to change. +``affinity_strict`` + 0 by default indicating that affinity scopes are not strict. When a work + item starts execution, workqueue makes a best-effort attempt to ensure + that the worker is inside its affinity scope, which is called + repatriation. Once started, the scheduler is free to move the worker + anywhere in the system as it sees fit. This enables benefiting from scope + locality while still being able to utilize other CPUs if necessary and + available. + + If set to 1, all workers of the scope are guaranteed always to be in the + scope. This may be useful when crossing affinity scopes has other + implications, for example, in terms of power consumption or workload + isolation. Strict NUMA scope can also be used to match the workqueue + behavior of older kernels. + Examining Configuration ======================= @@ -475,21 +491,21 @@ Monitoring Use tools/workqueue/wq_monitor.py to monitor workqueue operations: :: $ tools/workqueue/wq_monitor.py events - total infl CPUtime CPUhog CMwake mayday rescued + total infl CPUtime CPUhog CMW/RPR mayday rescued events 18545 0 6.1 0 5 - - events_highpri 8 0 0.0 0 0 - - events_long 3 0 0.0 0 0 - - - events_unbound 38306 0 0.1 - - - - + events_unbound 38306 0 0.1 - 7 - - events_freezable 0 0 0.0 0 0 - - events_power_efficient 29598 0 0.2 0 0 - - events_freezable_power_ 10 0 0.0 0 0 - - sock_diag_events 0 0 0.0 0 0 - - - total infl CPUtime CPUhog CMwake mayday rescued + total infl CPUtime CPUhog CMW/RPR mayday rescued events 18548 0 6.1 0 5 - - events_highpri 8 0 0.0 0 0 - - events_long 3 0 0.0 0 0 - - - events_unbound 38322 0 0.1 - - - - + events_unbound 38322 0 0.1 - 7 - - events_freezable 0 0 0.0 0 0 - - events_power_efficient 29603 0 0.2 0 0 - - events_freezable_power_ 10 0 0.0 0 0 - - diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index fe53976e088eb4..0c1cad38f9db61 100644 --- a/include/linux/workqueue.h +++ b/include/linux/workqueue.h @@ -169,6 +169,17 @@ struct workqueue_attrs { */ cpumask_var_t __pod_cpumask; + /** + * @affn_strict: affinity scope is strict + * + * If clear, workqueue will make a best-effort attempt at starting the + * worker inside @__pod_cpumask but the scheduler is free to migrate it + * outside. + * + * If set, workers are only allowed to run inside @__pod_cpumask. + */ + bool affn_strict; + /* * Below fields aren't properties of a worker_pool. They only modify how * :c:func:`apply_workqueue_attrs` select pools and thus don't diff --git a/kernel/workqueue.c b/kernel/workqueue.c index e61b4291bec858..6f6f4f37ceb324 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -211,6 +211,7 @@ enum pool_workqueue_stats { PWQ_STAT_CPU_TIME, /* total CPU time consumed */ PWQ_STAT_CPU_INTENSIVE, /* wq_cpu_intensive_thresh_us violations */ PWQ_STAT_CM_WAKEUP, /* concurrency-management worker wakeups */ + PWQ_STAT_REPATRIATED, /* unbound workers brought back into scope */ PWQ_STAT_MAYDAY, /* maydays to rescuer */ PWQ_STAT_RESCUED, /* linked work items executed by rescuer */ @@ -1103,13 +1104,41 @@ static bool assign_work(struct work_struct *work, struct worker *worker, static bool kick_pool(struct worker_pool *pool) { struct worker *worker = first_idle_worker(pool); + struct task_struct *p; lockdep_assert_held(&pool->lock); if (!need_more_worker(pool) || !worker) return false; - wake_up_process(worker->task); + p = worker->task; + +#ifdef CONFIG_SMP + /* + * Idle @worker is about to execute @work and waking up provides an + * opportunity to migrate @worker at a lower cost by setting the task's + * wake_cpu field. Let's see if we want to move @worker to improve + * execution locality. + * + * We're waking the worker that went idle the latest and there's some + * chance that @worker is marked idle but hasn't gone off CPU yet. If + * so, setting the wake_cpu won't do anything. As this is a best-effort + * optimization and the race window is narrow, let's leave as-is for + * now. If this becomes pronounced, we can skip over workers which are + * still on cpu when picking an idle worker. + * + * If @pool has non-strict affinity, @worker might have ended up outside + * its affinity scope. Repatriate. + */ + if (!pool->attrs->affn_strict && + !cpumask_test_cpu(p->wake_cpu, pool->attrs->__pod_cpumask)) { + struct work_struct *work = list_first_entry(&pool->worklist, + struct work_struct, entry); + p->wake_cpu = cpumask_any_distribute(pool->attrs->__pod_cpumask); + get_work_pwq(work)->stats[PWQ_STAT_REPATRIATED]++; + } +#endif + wake_up_process(p); return true; } @@ -2051,7 +2080,10 @@ static struct worker *alloc_worker(int node) static cpumask_t *pool_allowed_cpus(struct worker_pool *pool) { - return pool->attrs->__pod_cpumask; + if (pool->cpu < 0 && pool->attrs->affn_strict) + return pool->attrs->__pod_cpumask; + else + return pool->attrs->cpumask; } /** @@ -3715,6 +3747,7 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to, to->nice = from->nice; cpumask_copy(to->cpumask, from->cpumask); cpumask_copy(to->__pod_cpumask, from->__pod_cpumask); + to->affn_strict = from->affn_strict; /* * Unlike hash and equality test, copying shouldn't ignore wq-only @@ -3745,6 +3778,7 @@ static u32 wqattrs_hash(const struct workqueue_attrs *attrs) BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash); hash = jhash(cpumask_bits(attrs->__pod_cpumask), BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash); + hash = jhash_1word(attrs->affn_strict, hash); return hash; } @@ -3758,6 +3792,8 @@ static bool wqattrs_equal(const struct workqueue_attrs *a, return false; if (!cpumask_equal(a->__pod_cpumask, b->__pod_cpumask)) return false; + if (a->affn_strict != b->affn_strict) + return false; return true; } @@ -5847,6 +5883,7 @@ module_param_cb(default_affinity_scope, &wq_affn_dfl_ops, NULL, 0644); * nice RW int : nice value of the workers * cpumask RW mask : bitmask of allowed CPUs for the workers * affinity_scope RW str : worker CPU affinity scope (cache, numa, none) + * affinity_strict RW bool : worker CPU affinity is strict */ struct wq_device { struct workqueue_struct *wq; @@ -6026,10 +6063,42 @@ static ssize_t wq_affn_scope_store(struct device *dev, return ret ?: count; } +static ssize_t wq_affinity_strict_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + struct workqueue_struct *wq = dev_to_wq(dev); + + return scnprintf(buf, PAGE_SIZE, "%d\n", + wq->unbound_attrs->affn_strict); +} + +static ssize_t wq_affinity_strict_store(struct device *dev, + struct device_attribute *attr, + const char *buf, size_t count) +{ + struct workqueue_struct *wq = dev_to_wq(dev); + struct workqueue_attrs *attrs; + int v, ret = -ENOMEM; + + if (sscanf(buf, "%d", &v) != 1) + return -EINVAL; + + apply_wqattrs_lock(); + attrs = wq_sysfs_prep_attrs(wq); + if (attrs) { + attrs->affn_strict = (bool)v; + ret = apply_workqueue_attrs_locked(wq, attrs); + } + apply_wqattrs_unlock(); + free_workqueue_attrs(attrs); + return ret ?: count; +} + static struct device_attribute wq_sysfs_unbound_attrs[] = { __ATTR(nice, 0644, wq_nice_show, wq_nice_store), __ATTR(cpumask, 0644, wq_cpumask_show, wq_cpumask_store), __ATTR(affinity_scope, 0644, wq_affn_scope_show, wq_affn_scope_store), + __ATTR(affinity_strict, 0644, wq_affinity_strict_show, wq_affinity_strict_store), __ATTR_NULL, }; @@ -6452,6 +6521,7 @@ void __init workqueue_init_early(void) cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu)); cpumask_copy(pool->attrs->__pod_cpumask, cpumask_of(cpu)); pool->attrs->nice = std_nice[i++]; + pool->attrs->affn_strict = true; pool->node = cpu_to_node(cpu); /* alloc pool ID */ diff --git a/tools/workqueue/wq_dump.py b/tools/workqueue/wq_dump.py index 43ab71a193b836..d0df5833f2c185 100644 --- a/tools/workqueue/wq_dump.py +++ b/tools/workqueue/wq_dump.py @@ -36,10 +36,11 @@ Lists all workqueues along with their type and worker pool association. For each workqueue: - NAME TYPE POOL_ID... + NAME TYPE[,FLAGS] POOL_ID... NAME name of the workqueue TYPE percpu, unbound or ordered + FLAGS S: strict affinity scope POOL_ID worker pool ID associated with each possible CPU """ @@ -138,13 +139,16 @@ def print_pod_type(pt): print(f'cpu={pool.cpu.value_():3}', end='') else: print(f'cpus={cpumask_str(pool.attrs.cpumask)}', end='') + print(f' pod_cpus={cpumask_str(pool.attrs.__pod_cpumask)}', end='') + if pool.attrs.affn_strict: + print(' strict', end='') print('') print('') print('Workqueue CPU -> pool') print('=====================') -print('[ workqueue \ CPU ', end='') +print('[ workqueue \ type CPU', end='') for cpu in for_each_possible_cpu(prog): print(f' {cpu:{max_pool_id_len}}', end='') print(' dfl]') @@ -153,11 +157,15 @@ def print_pod_type(pt): print(f'{wq.name.string_().decode()[-24:]:24}', end='') if wq.flags & WQ_UNBOUND: if wq.flags & WQ_ORDERED: - print(' ordered', end='') + print(' ordered ', end='') else: print(' unbound', end='') + if wq.unbound_attrs.affn_strict: + print(',S ', end='') + else: + print(' ', end='') else: - print(' percpu ', end='') + print(' percpu ', end='') for cpu in for_each_possible_cpu(prog): pool_id = per_cpu_ptr(wq.cpu_pwq, cpu)[0].pool.id.value_() diff --git a/tools/workqueue/wq_monitor.py b/tools/workqueue/wq_monitor.py index 6e258d123e8c7f..a8856a9c45dcc9 100644 --- a/tools/workqueue/wq_monitor.py +++ b/tools/workqueue/wq_monitor.py @@ -20,8 +20,11 @@ and got excluded from concurrency management to avoid stalling other work items. - CMwake The number of concurrency-management wake-ups while executing a - work item of the workqueue. + CMW/RPR For per-cpu workqueues, the number of concurrency-management + wake-ups while executing a work item of the workqueue. For + unbound workqueues, the number of times a worker was repatriated + to its affinity scope after being migrated to an off-scope CPU by + the scheduler. mayday The number of times the rescuer was requested while waiting for new worker creation. @@ -65,6 +68,7 @@ def err(s): PWQ_STAT_CPU_TIME = prog['PWQ_STAT_CPU_TIME'] # total CPU time consumed PWQ_STAT_CPU_INTENSIVE = prog['PWQ_STAT_CPU_INTENSIVE'] # wq_cpu_intensive_thresh_us violations PWQ_STAT_CM_WAKEUP = prog['PWQ_STAT_CM_WAKEUP'] # concurrency-management worker wakeups +PWQ_STAT_REPATRIATED = prog['PWQ_STAT_REPATRIATED'] # unbound workers brought back into scope PWQ_STAT_MAYDAY = prog['PWQ_STAT_MAYDAY'] # maydays to rescuer PWQ_STAT_RESCUED = prog['PWQ_STAT_RESCUED'] # linked work items executed by rescuer PWQ_NR_STATS = prog['PWQ_NR_STATS'] @@ -89,22 +93,25 @@ def dict(self, now): 'cpu_time' : self.stats[PWQ_STAT_CPU_TIME], 'cpu_intensive' : self.stats[PWQ_STAT_CPU_INTENSIVE], 'cm_wakeup' : self.stats[PWQ_STAT_CM_WAKEUP], + 'repatriated' : self.stats[PWQ_STAT_REPATRIATED], 'mayday' : self.stats[PWQ_STAT_MAYDAY], 'rescued' : self.stats[PWQ_STAT_RESCUED], } def table_header_str(): return f'{"":>24} {"total":>8} {"infl":>5} {"CPUtime":>8} '\ - f'{"CPUitsv":>7} {"CMwake":>7} {"mayday":>7} {"rescued":>7}' + f'{"CPUitsv":>7} {"CMW/RPR":>7} {"mayday":>7} {"rescued":>7}' def table_row_str(self): cpu_intensive = '-' - cm_wakeup = '-' + cmw_rpr = '-' mayday = '-' rescued = '-' - if not self.unbound: + if self.unbound: + cmw_rpr = str(self.stats[PWQ_STAT_REPATRIATED]); + else: cpu_intensive = str(self.stats[PWQ_STAT_CPU_INTENSIVE]) - cm_wakeup = str(self.stats[PWQ_STAT_CM_WAKEUP]) + cmw_rpr = str(self.stats[PWQ_STAT_CM_WAKEUP]) if self.mem_reclaim: mayday = str(self.stats[PWQ_STAT_MAYDAY]) @@ -115,7 +122,7 @@ def table_row_str(self): f'{max(self.stats[PWQ_STAT_STARTED] - self.stats[PWQ_STAT_COMPLETED], 0):5} ' \ f'{self.stats[PWQ_STAT_CPU_TIME] / 1000000:8.1f} ' \ f'{cpu_intensive:>7} ' \ - f'{cm_wakeup:>7} ' \ + f'{cmw_rpr:>7} ' \ f'{mayday:>7} ' \ f'{rescued:>7} ' return out.rstrip(':')