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authorSuresh Siddha <suresh.b.siddha@intel.com>2008-10-30 13:28:41 -0400
committerJens Axboe <jens.axboe@oracle.com>2008-11-06 02:41:56 -0500
commit561920a0d2bb6d63343e83acfd784c0a77bd28d1 (patch)
tree7b87d9d867296d4a14e9b287129fcfd0b2cd1b47 /kernel
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/smp.c18
1 files changed, 12 insertions, 6 deletions
diff --git a/kernel/smp.c b/kernel/smp.c
index f362a8553777..75c8dde58c55 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -51,10 +51,6 @@ static void csd_flag_wait(struct call_single_data *data)
51{ 51{
52 /* Wait for response */ 52 /* Wait for response */
53 do { 53 do {
54 /*
55 * We need to see the flags store in the IPI handler
56 */
57 smp_mb();
58 if (!(data->flags & CSD_FLAG_WAIT)) 54 if (!(data->flags & CSD_FLAG_WAIT))
59 break; 55 break;
60 cpu_relax(); 56 cpu_relax();
@@ -76,6 +72,11 @@ static void generic_exec_single(int cpu, struct call_single_data *data)
76 list_add_tail(&data->list, &dst->list); 72 list_add_tail(&data->list, &dst->list);
77 spin_unlock_irqrestore(&dst->lock, flags); 73 spin_unlock_irqrestore(&dst->lock, flags);
78 74
75 /*
76 * Make the list addition visible before sending the ipi.
77 */
78 smp_mb();
79
79 if (ipi) 80 if (ipi)
80 arch_send_call_function_single_ipi(cpu); 81 arch_send_call_function_single_ipi(cpu);
81 82
@@ -157,7 +158,7 @@ void generic_smp_call_function_single_interrupt(void)
157 * Need to see other stores to list head for checking whether 158 * Need to see other stores to list head for checking whether
158 * list is empty without holding q->lock 159 * list is empty without holding q->lock
159 */ 160 */
160 smp_mb(); 161 smp_read_barrier_depends();
161 while (!list_empty(&q->list)) { 162 while (!list_empty(&q->list)) {
162 unsigned int data_flags; 163 unsigned int data_flags;
163 164
@@ -191,7 +192,7 @@ void generic_smp_call_function_single_interrupt(void)
191 /* 192 /*
192 * See comment on outer loop 193 * See comment on outer loop
193 */ 194 */
194 smp_mb(); 195 smp_read_barrier_depends();
195 } 196 }
196} 197}
197 198
@@ -370,6 +371,11 @@ int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
370 list_add_tail_rcu(&data->csd.list, &call_function_queue); 371 list_add_tail_rcu(&data->csd.list, &call_function_queue);
371 spin_unlock_irqrestore(&call_function_lock, flags); 372 spin_unlock_irqrestore(&call_function_lock, flags);
372 373
374 /*
375 * Make the list addition visible before sending the ipi.
376 */
377 smp_mb();
378
373 /* Send a message to all CPUs in the map */ 379 /* Send a message to all CPUs in the map */
374 arch_send_call_function_ipi(mask); 380 arch_send_call_function_ipi(mask);
375 381