[PATCH 3/3] scsi: align scsi_device iodone_cnt to avoid cache line contention

[Sumit Saxena <sumit.saxena@broadcom.com>]

From: James Rizzo <james.rizzo@broadcom.com>

Place iodone_cnt on its own cache line so it does not share a cache line
with iorequest_cnt, avoiding significant performance hits from false
sharing when request and completion paths update these counters on some
CPU architectures.

Signed-off-by: James Rizzo <james.rizzo@broadcom.com>
Signed-off-by: Sumit Saxena <sumit.saxena@broadcom.com>
---
 include/scsi/scsi_device.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 9c2a7bbe5891..86c2a3a6b206 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -272,7 +272,9 @@ struct scsi_device {
 #define SCSI_DEFAULT_DEVICE_BLOCKED	3
 
 	atomic_t iorequest_cnt;
-	atomic_t iodone_cnt;
+	/* ensure iorequest_cnt and iodone_cnt are on different cache lines to avoid significant
+	   performance hits on cache line contention on some CPU architectures */
+	atomic_t iodone_cnt ____cacheline_aligned_in_smp;
 	atomic_t ioerr_cnt;
 	atomic_t iotmo_cnt;
 
-- 
2.43.7