[Open-FCoE] [PATCH] fcoe: Add sysfs parameter to fcoe for minimum DDP read I/O size

Yi Zou yi.zou at intel.com
Wed Jul 15 23:38:45 UTC 2009

This adds fcoe_ddp_min as a module parameter for fcoe module to:

It is observed that for some hardware, particularly Intel 825599, there is too
much overhead in setting up context for direct data placement (DDP) read when
the requested read I/O size is small. This is added as a module parameter for
performance tuning and is set as 0 by default and user can change this based
on their own hardware.

Signed-off-by: Yi Zou <yi.zou at intel.com>

 drivers/scsi/fcoe/fcoe.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/drivers/scsi/fcoe/fcoe.c b/drivers/scsi/fcoe/fcoe.c
index e01ee83..9abd00c 100644
--- a/drivers/scsi/fcoe/fcoe.c
+++ b/drivers/scsi/fcoe/fcoe.c
@@ -49,6 +49,12 @@ MODULE_AUTHOR("Open-FCoE.org");
+/* Performance tuning parameters for fcoe */
+static unsigned int fcoe_ddp_min;
+module_param(fcoe_ddp_min, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(fcoe_ddp_min, "Minimum I/O size in bytes for "	\
+		 "Direct Data Placement (DDP).");
 /* fcoe host list */
@@ -420,7 +426,8 @@ static int fcoe_shost_config(struct fc_lport *lp, struct Scsi_Host *shost,
 bool fcoe_oem_match(struct fc_frame *fp)
-	return fc_fcp_is_read(fr_fsp(fp));
+	return fc_fcp_is_read(fr_fsp(fp)) &&
+		(fr_fsp(fp)->data_len > fcoe_ddp_min);

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