[PATCH 05/19] s390/dasd: Optimize max blocks per request for track alignment

Stefan Haberland <[email protected]> Wed, 5 Aug 2026 13:15:58 +0200

Newsgroups	org.kernel.vger.linux-block,org.kernel.vger.linux-s390
Message-ID	<[email protected]>

With 4096-byte blocks a full ECKD track holds exactly 12 records. Lower
DASD_ECKD_MAX_BLOCKS from 190 to 180 so requests align to track
boundaries (15 full tracks); full-track I/O is more efficient than
partial-track writes, and 190 had no alignment significance and could
let a request cross a track boundary.

Reviewed-by: Jan Höppner <[email protected]>
Signed-off-by: Stefan Haberland <[email protected]>
---
 drivers/s390/block/dasd_eckd.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/block/dasd_eckd.h b/drivers/s390/block/dasd_eckd.h
index f9299bd184ba..763733bcc4d2 100644
--- a/drivers/s390/block/dasd_eckd.h
+++ b/drivers/s390/block/dasd_eckd.h
@@ -131,7 +131,7 @@
 /*
  * Maximum number of blocks to be chained
  */
-#define DASD_ECKD_MAX_BLOCKS		 190
+#define DASD_ECKD_MAX_BLOCKS		 180
 #define DASD_ECKD_MAX_BLOCKS_RAW	 256
 
 /*****************************************************************************
-- 
2.53.0