s390/cio: More efficient handling of CHPID availability events
The CIO layer processes hardware events that indicate that a channel
path has become available by performing a scan of available subchannels
using the Store Subchannel (STSCH) instruction. Performing too many
STSCH instructions in a tight loop can cause high Hypervisor overhead
which can negatively impact the performance of the virtual machine as
a whole.
This patch reduces the number of STSCH instructions performed while
processing a resource accessibility event and while varying a CHPID
online.
In both cases, Linux first performs a STSCH instruction on each unused
subchannel to see if the subchannel has become available. If the STSCH
instruction indicates that the subchannel is available, a full
evaluation of this subchannel is scheduled. Since the full evaluation
includes performing a STSCH instruction, the initial STSCH is
unnecessary and can be removed.
Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Reviewed-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/cio/chsc.c b/drivers/s390/cio/chsc.c
index 13299f9..eee70cb 100644
--- a/drivers/s390/cio/chsc.c
+++ b/drivers/s390/cio/chsc.c
@@ -237,26 +237,6 @@
for_each_subchannel_staged(s390_subchannel_remove_chpid, NULL, &link);
}
-static int s390_process_res_acc_new_sch(struct subchannel_id schid, void *data)
-{
- struct schib schib;
- /*
- * We don't know the device yet, but since a path
- * may be available now to the device we'll have
- * to do recognition again.
- * Since we don't have any idea about which chpid
- * that beast may be on we'll have to do a stsch
- * on all devices, grr...
- */
- if (stsch_err(schid, &schib))
- /* We're through */
- return -ENXIO;
-
- /* Put it on the slow path. */
- css_schedule_eval(schid);
- return 0;
-}
-
static int __s390_process_res_acc(struct subchannel *sch, void *data)
{
spin_lock_irq(sch->lock);
@@ -287,8 +267,8 @@
* The more information we have (info), the less scanning
* will we have to do.
*/
- for_each_subchannel_staged(__s390_process_res_acc,
- s390_process_res_acc_new_sch, link);
+ for_each_subchannel_staged(__s390_process_res_acc, NULL, link);
+ css_schedule_reprobe();
}
static int
@@ -663,19 +643,6 @@
return 0;
}
-static int
-__s390_vary_chpid_on(struct subchannel_id schid, void *data)
-{
- struct schib schib;
-
- if (stsch_err(schid, &schib))
- /* We're through */
- return -ENXIO;
- /* Put it on the slow path. */
- css_schedule_eval(schid);
- return 0;
-}
-
/**
* chsc_chp_vary - propagate channel-path vary operation to subchannels
* @chpid: channl-path ID
@@ -694,7 +661,8 @@
/* Try to update the channel path description. */
chp_update_desc(chp);
for_each_subchannel_staged(s390_subchannel_vary_chpid_on,
- __s390_vary_chpid_on, &chpid);
+ NULL, &chpid);
+ css_schedule_reprobe();
} else
for_each_subchannel_staged(s390_subchannel_vary_chpid_off,
NULL, &chpid);
