[azure][PATCH 3/3] UBUNTU: SAUCE: scsi: storvsc: Spread interrupts when picking a channel for I/O requests

[Marcelo Henrique Cerri]

From: Michael Kelley <mikelley at ntdev.microsoft.com>

BugLink: http://bugs.launchpad.net/bugs/1745260

Update the algorithm in storvsc_do_io to look for a channel
starting with the current CPU + 1 and wrap around (within the
current NUMA node). This spreads VMbus interrupts more evenly
across CPUs. Previous code always started with first CPU in
the current NUMA node, skewing the interrupt load to that CPU.

Signed-off-by: Michael Kelley <mikelley at microsoft.com>
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 drivers/scsi/storvsc_drv.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 57a6e16e7741..d4df3a6f4c62 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1314,7 +1314,8 @@ static int storvsc_do_io(struct hv_device *device,
 			 */
 			cpumask_and(&alloced_mask, &stor_device->alloced_cpus,
 				    cpumask_of_node(cpu_to_node(q_num)));
-			for_each_cpu(tgt_cpu, &alloced_mask) {
+			for_each_cpu_wrap(tgt_cpu, &alloced_mask,
+					outgoing_channel->target_cpu + 1) {
 				if (tgt_cpu != outgoing_channel->target_cpu) {
 					outgoing_channel =
 					stor_device->stor_chns[tgt_cpu];
-- 
2.7.4