[S390] cio: reduce cpu utilization during device scan

Minimize calls to cpu intensive function get_subchannel_by_schid()
by introducing function for_each_subchannel_staged() which
temporarily caches the information about registered subchannels
in a bitmap.

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/s390/cio/css.h b/drivers/s390/cio/css.h
index 40598b8ee27d..b70554523552 100644
--- a/drivers/s390/cio/css.h
+++ b/drivers/s390/cio/css.h
@@ -91,6 +91,9 @@ extern void css_driver_unregister(struct css_driver *);
 extern void css_sch_device_unregister(struct subchannel *);
 extern struct subchannel * get_subchannel_by_schid(struct subchannel_id);
 extern int css_init_done;
+int for_each_subchannel_staged(int (*fn_known)(struct subchannel *, void *),
+                               int (*fn_unknown)(struct subchannel_id,
+                               void *), void *data);
 extern int for_each_subchannel(int(*fn)(struct subchannel_id, void *), void *);
 extern void css_process_crw(int, int);
 extern void css_reiterate_subchannels(void);