s390/dasd: mark DASD devices as non rotational

We were able to reduce the CPU overhead of big paging scenarios
when announcing our paging disks as non-rotational.
Almost all dasd devices are implemented in storage servers with
cache, raid, striping and lots of magic. There is no point in
optimizing the disk schedulers and swap code for a single platter
moving arm rotational disks. Given the complexity of the setup
and the fact that this change is mostly to disable the additional
overhead in swap code, lets keep the other functionality unchanged
and do not disable the this device as entropy source - unlike other
non-rotational devices.

Suggested-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index f73d2f579a7ef26f053eb5d314dd71e54ed60b82..a263c10359e1553f007a1a031e8b76733c463109 100644 (file)
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -3030,6 +3030,7 @@ static void dasd_setup_queue(struct dasd_block *block)
        } else {
                max = block->base->discipline->max_blocks << block->s2b_shift;
        }
+       queue_flag_set_unlocked(QUEUE_FLAG_NONROT, block->request_queue);
        blk_queue_logical_block_size(block->request_queue,
                                     block->bp_block);
        blk_queue_max_hw_sectors(block->request_queue, max);