There was some concern that using multiple queues - and their
associated APIC vectors - may trigger bugs in various dubious APIC
implementations. This patch adds a command line option to force the
kernel to use a single queue, even if the architecture can support
more.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
Documentation/kernel-parameters.txt | 5 +++++
arch/x86/kernel/smp.c | 2 +-
arch/x86/xen/smp.c | 6 ++++--
include/linux/smp.h | 26 ++++++++++++++++++++++++++
kernel/smp.c | 14 +++++++++++++-
5 files changed, 49 insertions(+), 4 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1894,6 +1894,11 @@
simeth= [IA-64]
simscsi=
+ single_ipi_queue [X86]
+ Force the use of a single queue for smp function calls.
+ This means that only a single vector is used, which may avoid
+ bugs in some APIC implementations.
+
slram= [HW,MTD]
slub_debug[=options[,slabs]] [MM, SLUB]
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -129,7 +129,7 @@
void native_send_call_func_ipi(cpumask_t mask)
{
cpumask_t allbutself;
- unsigned queue = smp_processor_id() % CONFIG_GENERIC_SMP_QUEUES;
+ unsigned queue = smp_ipi_choose_queue();
allbutself = cpu_online_map;
cpu_clear(smp_processor_id(), allbutself);
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -373,7 +373,7 @@
static void xen_smp_send_call_function_ipi(cpumask_t mask)
{
int cpu;
- unsigned queue = smp_processor_id() % CONFIG_GENERIC_SMP_QUEUES;
+ unsigned queue = smp_ipi_choose_queue();
/*
* We can't afford to allocate N callfunc vectors * M cpu
@@ -411,10 +411,12 @@
unsigned queue;
irq_enter();
+
queue = start_queue;
do {
generic_smp_call_function_interrupt(queue);
- queue = (queue + 1) % CONFIG_GENERIC_SMP_QUEUES;
+ if (++queue == smp_ipi_nqueues())
+ queue = 0;
} while(queue != start_queue);
#ifdef CONFIG_X86_32
diff --git a/include/linux/smp.h b/include/linux/smp.h
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -168,4 +168,30 @@
void smp_setup_processor_id(void);
+#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
+extern bool __read_mostly smp_single_ipi_queue;
+
+static inline unsigned smp_ipi_nqueues(void)
+{
+ unsigned nqueues = 1;
+
+#ifdef CONFIG_GENERIC_SMP_QUEUES
+ nqueues = CONFIG_GENERIC_SMP_QUEUES;
+#endif
+
+ return nqueues;
+}
+
+static inline unsigned smp_ipi_choose_queue(void)
+{
+ unsigned cpu = smp_processor_id();
+ unsigned nqueues = smp_ipi_nqueues();
+
+ if (nqueues == 1 || smp_single_ipi_queue)
+ return 0;
+
+ return cpu % nqueues;
+}
+#endif
+
#endif /* __LINUX_SMP_H */
diff --git a/kernel/smp.c b/kernel/smp.c
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -10,6 +10,8 @@
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/smp.h>
+
+bool __read_mostly smp_single_ipi_queue = false;
#ifdef CONFIG_GENERIC_SMP_QUEUES
#define NQUEUES CONFIG_GENERIC_SMP_QUEUES
@@ -310,7 +312,7 @@
cpus_and(mask, mask, allbutself);
num_cpus = cpus_weight(mask);
- queue_no = cpu % NQUEUES;
+ queue_no = smp_ipi_choose_queue();
queue = &call_function_queues[queue_no];
/*
@@ -424,6 +426,16 @@
spin_lock_init(&call_function_queues[i].lock);
}
+ printk(KERN_INFO "smp function calls: using %d/%d queues\n",
+ smp_ipi_nqueues(), NQUEUES);
+
return 0;
}
early_initcall(init_smp_function_call);
+
+static __init int set_single_ipi_queue(char *str)
+{
+ smp_single_ipi_queue = true;
+ return 0;
+}
+early_param("single_ipi_queue", set_single_ipi_queue);
--
