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-rw-r--r--Documentation/kernel-parameters.txt11
-rw-r--r--kernel/workqueue.c23
-rw-r--r--lib/Kconfig.debug15
3 files changed, 47 insertions, 2 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 87d40a72f6a1..cda2ead39093 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -4230,6 +4230,17 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
The default value of this parameter is determined by
the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
+ workqueue.debug_force_rr_cpu
+ Workqueue used to implicitly guarantee that work
+ items queued without explicit CPU specified are put
+ on the local CPU. This guarantee is no longer true
+ and while local CPU is still preferred work items
+ may be put on foreign CPUs. This debug option
+ forces round-robin CPU selection to flush out
+ usages which depend on the now broken guarantee.
+ When enabled, memory and cache locality will be
+ impacted.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 054774605d2f..51d77e7c0989 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -307,6 +307,18 @@ static cpumask_var_t wq_unbound_cpumask;
/* CPU where unbound work was last round robin scheduled from this CPU */
static DEFINE_PER_CPU(int, wq_rr_cpu_last);
+/*
+ * Local execution of unbound work items is no longer guaranteed. The
+ * following always forces round-robin CPU selection on unbound work items
+ * to uncover usages which depend on it.
+ */
+#ifdef CONFIG_DEBUG_WQ_FORCE_RR_CPU
+static bool wq_debug_force_rr_cpu = true;
+#else
+static bool wq_debug_force_rr_cpu = false;
+#endif
+module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);
+
/* the per-cpu worker pools */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
cpu_worker_pools);
@@ -1309,10 +1321,17 @@ static bool is_chained_work(struct workqueue_struct *wq)
*/
static int wq_select_unbound_cpu(int cpu)
{
+ static bool printed_dbg_warning;
int new_cpu;
- if (cpumask_test_cpu(cpu, wq_unbound_cpumask))
- return cpu;
+ if (likely(!wq_debug_force_rr_cpu)) {
+ if (cpumask_test_cpu(cpu, wq_unbound_cpumask))
+ return cpu;
+ } else if (!printed_dbg_warning) {
+ pr_warn("workqueue: round-robin CPU selection forced, expect performance impact\n");
+ printed_dbg_warning = true;
+ }
+
if (cpumask_empty(wq_unbound_cpumask))
return cpu;
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ecb9e75614bf..8bfd1aca7a3d 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1400,6 +1400,21 @@ config RCU_EQS_DEBUG
endmenu # "RCU Debugging"
+config DEBUG_WQ_FORCE_RR_CPU
+ bool "Force round-robin CPU selection for unbound work items"
+ depends on DEBUG_KERNEL
+ default n
+ help
+ Workqueue used to implicitly guarantee that work items queued
+ without explicit CPU specified are put on the local CPU. This
+ guarantee is no longer true and while local CPU is still
+ preferred work items may be put on foreign CPUs. Kernel
+ parameter "workqueue.debug_force_rr_cpu" is added to force
+ round-robin CPU selection to flush out usages which depend on the
+ now broken guarantee. This config option enables the debug
+ feature by default. When enabled, memory and cache locality will
+ be impacted.
+
config DEBUG_BLOCK_EXT_DEVT
bool "Force extended block device numbers and spread them"
depends on DEBUG_KERNEL