lightnvm: pblk: enable 1 LUN configuration
Metadata I/Os are scheduled to minimize their impact on user data I/Os.
When there are enough LUNs instantiated (i.e., enough bandwidth), it is
easy to interleave metadata and data one after the other so that
metadata I/Os are the ones being blocked and not vice-versa.
We do this by calculating the distance between the I/Os in terms of the
LUNs that are not in used, and selecting a free LUN that satisfies a
the simple heuristic that metadata is scheduled behind. The per-LUN
semaphores guarantee consistency. This works fine on >1 LUN
configuration. However, when a single LUN is instantiated, this design
leads to a deadlock, where metadata waits to be scheduled on a free LUN.
This patch implements the 1 LUN case by simply scheduling the metadada
I/O after the data I/O. In the process, we refactor the way a line is
replaced to ensure that metadata writes are submitted after data writes
in order to guarantee block sequentiality. Note that, since there is
only one LUN, both I/Os will block each other by design. However, such
configuration only pursues tight read latencies, not write bandwidth.
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c
index 3452764..3c37491 100644
--- a/drivers/lightnvm/pblk-init.c
+++ b/drivers/lightnvm/pblk-init.c
@@ -711,8 +711,12 @@ static int pblk_lines_init(struct pblk *pblk)
}
lm->emeta_bb = geo->nr_luns - i;
- lm->min_blk_line = 1 + DIV_ROUND_UP(lm->smeta_sec + lm->emeta_sec[0],
- geo->sec_per_blk);
+
+ lm->min_blk_line = 1;
+ if (geo->nr_luns > 1)
+ lm->min_blk_line += DIV_ROUND_UP(lm->smeta_sec +
+ lm->emeta_sec[0], geo->sec_per_blk);
+
if (lm->min_blk_line > lm->blk_per_line) {
pr_err("pblk: config. not supported. Min. LUN in line:%d\n",
lm->blk_per_line);