Added description of the zones_wlock tunable attribute. Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx> --- Documentation/block/deadline-iosched.txt | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/Documentation/block/deadline-iosched.txt b/Documentation/block/deadline-iosched.txt index 2d82c80322cb..b532304d2bf4 100644 --- a/Documentation/block/deadline-iosched.txt +++ b/Documentation/block/deadline-iosched.txt @@ -69,6 +69,23 @@ Front merges may still occur due to the cached last_merge hint, but since that comes at basically 0 cost we leave that on. We simply disable the rbtree front sector lookup when the io scheduler merge function is called. +zones_wlock (bool) +----------- + +(mq-deadlines only) +The blk-mq version of the deadline I/O scheduler, mq-deadline, introduced +support for zoned block devices. This added support prevents dispatching of more +than one write command per zone of the device to avoid write sequence reordering +due to the possible concurrent execution of many blk-mq operations, in +particular request dispatching. This is achieved using a per zone lock +implemented as a bitmap. When a write request is dispatched, the target zone of +the request is locked, preventing further dispatch of write requests to it +(there are no limitations on read commands). The zones_wlock tunable allows +disabling zone write locking for host aware zoned block devices as these drive +can handle random writes to zones in firmware. This tunable default setting +cannot be changed for host managed disks (always enabled) and regular disks +(always disabled). + Nov 11 2002, Jens Axboe <jens.axboe@xxxxxxxxxx> -- 2.13.5
