Re: [PATCH v2 6/6] dm mpath: delay the requeue of blk-mq requests while all paths down

On 09/14/2016 06:29 PM, Mike Snitzer wrote:

Return DM_MAPIO_DELAY_REQUEUE from .clone_and_map_rq.  Also, return
false from .busy, if all paths are down, so that blk-mq requests get
mapped via .clone_and_map_rq -- which results in DM_MAPIO_DELAY_REQUEUE
being returned to dm-rq.

This change allows for a noticeable reduction in cpu utilization
(reduced kworker load) while all paths are down, e.g.:

system CPU idleness (as measured by fio's --idle-prof=system):
before: system: 86.58%
after:  system: 98.60%

Signed-off-by: Mike Snitzer <redacted>
---
 drivers/md/dm-mpath.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

Reviewed-by: Hannes Reinecke <hare@suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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