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dm mpath: add start_io and nr_bytes to path selectors

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This patch makes two additions to the dm path selector interface for
dynamic load balancers:
  o a new hook, start_io()
  o a new parameter 'nr_bytes' to select_path()/start_io()/end_io()
    to pass the size of the I/O

start_io() is called when a target driver actually submits I/O
to the selected path.
Path selectors can use it to start accounting of the I/O.
(e.g. counting the number of in-flight I/Os.)
The start_io hook is based on the patch posted by Stefan Bader:
https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html

nr_bytes, the size of the I/O, is so path selectors can take the
size of the I/O into account when deciding which path to use.
dm-service-time uses it to estimate service time, for example.
(Added the nr_bytes member to dm_mpath_io instead of using existing
 details.bi_size, since request-based dm patch deletes it.)

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Kiyoshi Ueda
2009-06-22 10:12:27 +01:00
committed by Alasdair G Kergon
parent 2bd0234525
commit 02ab823fd1
3 changed files with 25 additions and 13 deletions
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8
drivers/md/dm-path-selector.h
View File

@@ -56,7 +56,8 @@ struct path_selector_type {
* the path fails.
*/
struct dm_path *(*select_path) (struct path_selector *ps,
unsigned *repeat_count);
unsigned *repeat_count,
size_t nr_bytes);
/*
* Notify the selector that a path has failed.
@@ -75,7 +76,10 @@ struct path_selector_type {
int (*status) (struct path_selector *ps, struct dm_path *path,
status_type_t type, char *result, unsigned int maxlen);
int (*end_io) (struct path_selector *ps, struct dm_path *path);
int (*start_io) (struct path_selector *ps, struct dm_path *path,
size_t nr_bytes);
int (*end_io) (struct path_selector *ps, struct dm_path *path,
size_t nr_bytes);
};
/* Register a path selector */