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authorSuresh Siddha <suresh.b.siddha@intel.com>2008-10-30 18:28:41 +0100
committerJens Axboe <jens.axboe@oracle.com>2008-11-06 08:41:56 +0100
commit561920a0d2bb6d63343e83acfd784c0a77bd28d1 (patch)
tree7b87d9d867296d4a14e9b287129fcfd0b2cd1b47
parente78042e5b83936b1d12a4b5bbb492bdd88ad76c6 (diff)
generic-ipi: fix the smp_mb() placement
smp_mb() is needed (to make the memory operations visible globally) before sending the ipi on the sender and the receiver (on Alpha atleast) needs smp_read_barrier_depends() in the handler before reading the call_single_queue list in a lock-free fashion. On x86, x2apic mode register accesses for sending IPI's don't have serializing semantics. So the need for smp_mb() before sending the IPI becomes more critical in x2apic mode. Remove the unnecessary smp_mb() in csd_flag_wait(), as the presence of that smp_mb() doesn't mean anything on the sender, when the ipi receiver is not doing any thing special (like memory fence) after clearing the CSD_FLAG_WAIT. Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
-rw-r--r--kernel/smp.c18
1 files changed, 12 insertions, 6 deletions
diff --git a/kernel/smp.c b/kernel/smp.c
index f362a855377..75c8dde58c5 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -51,10 +51,6 @@ static void csd_flag_wait(struct call_single_data *data)
{
/* Wait for response */
do {
- /*
- * We need to see the flags store in the IPI handler
- */
- smp_mb();
if (!(data->flags & CSD_FLAG_WAIT))
break;
cpu_relax();
@@ -76,6 +72,11 @@ static void generic_exec_single(int cpu, struct call_single_data *data)
list_add_tail(&data->list, &dst->list);
spin_unlock_irqrestore(&dst->lock, flags);
+ /*
+ * Make the list addition visible before sending the ipi.
+ */
+ smp_mb();
+
if (ipi)
arch_send_call_function_single_ipi(cpu);
@@ -157,7 +158,7 @@ void generic_smp_call_function_single_interrupt(void)
* Need to see other stores to list head for checking whether
* list is empty without holding q->lock
*/
- smp_mb();
+ smp_read_barrier_depends();
while (!list_empty(&q->list)) {
unsigned int data_flags;
@@ -191,7 +192,7 @@ void generic_smp_call_function_single_interrupt(void)
/*
* See comment on outer loop
*/
- smp_mb();
+ smp_read_barrier_depends();
}
}
@@ -370,6 +371,11 @@ int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
list_add_tail_rcu(&data->csd.list, &call_function_queue);
spin_unlock_irqrestore(&call_function_lock, flags);
+ /*
+ * Make the list addition visible before sending the ipi.
+ */
+ smp_mb();
+
/* Send a message to all CPUs in the map */
arch_send_call_function_ipi(mask);