[SCSI] aacraid: 17 element sg performance update

Received From Mark Salyzyn.

The Jaguar and Corsair class of adapters (2410, 2810, 2610, 21610, CERC)
perform better (about 10% better read performance, write performance
neutral) with current Firmware if the OS limits the number of scatter
gather elements to 17 per request.

Signed-off-by: Mark Haverkamp <markh@osdl.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/scsi/aacraid/aacraid.h b/drivers/scsi/aacraid/aacraid.h
index 30fd8d6e3f31..66dbb6d2c506 100644
--- a/drivers/scsi/aacraid/aacraid.h
+++ b/drivers/scsi/aacraid/aacraid.h
@@ -532,6 +532,13 @@ struct aac_driver_ident
 #define AAC_QUIRK_MASTER 0x0008
 
 /*
+ * Some adapter firmware perform poorly when it must split up scatter gathers
+ * in order to deal with the limits of the underlying CHIM. This limit in this
+ * class of adapters is 17 scatter gather elements.
+ */
+#define AAC_QUIRK_17SG  0x0010
+
+/*
  *      The adapter interface specs all queues to be located in the same
  *      physically contigous block. The host structure that defines the
  *      commuication queues will assume they are each a separate physically