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s390/cio: More efficient handling of CHPID availability events

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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>
This commit is contained in:
Peter Oberparleiter 2013-11-26 14:55:56 +01:00 • committed by Martin Schwidefsky
parent 319e2e3f63
commit 449666dd1e
1 changed files with 4 additions and 36 deletions
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40
drivers/s390/cio/chsc.c
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@ -237,26 +237,6 @@ void chsc_chp_offline(struct chp_id chpid)
for_each_subchannel_staged(s390_subchannel_remove_chpid, NULL, &link); 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) static int __s390_process_res_acc(struct subchannel *sch, void *data)
{ {
spin_lock_irq(sch->lock); spin_lock_irq(sch->lock);
@ -287,8 +267,8 @@ static void s390_process_res_acc(struct chp_link *link)
* The more information we have (info), the less scanning * The more information we have (info), the less scanning
* will we have to do. * will we have to do.
*/ */
for_each_subchannel_staged(__s390_process_res_acc, for_each_subchannel_staged(__s390_process_res_acc, NULL, link);
s390_process_res_acc_new_sch, link); css_schedule_reprobe();
} }
static int static int
@ -663,19 +643,6 @@ static int s390_subchannel_vary_chpid_on(struct subchannel *sch, void *data)
return 0; 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 * chsc_chp_vary - propagate channel-path vary operation to subchannels
* @chpid: channl-path ID * @chpid: channl-path ID
@ -694,7 +661,8 @@ int chsc_chp_vary(struct chp_id chpid, int on)
/* Try to update the channel path description. */ /* Try to update the channel path description. */
chp_update_desc(chp); chp_update_desc(chp);
for_each_subchannel_staged(s390_subchannel_vary_chpid_on, for_each_subchannel_staged(s390_subchannel_vary_chpid_on,
__s390_vary_chpid_on, &chpid); NULL, &chpid);
css_schedule_reprobe();
} else } else
for_each_subchannel_staged(s390_subchannel_vary_chpid_off, for_each_subchannel_staged(s390_subchannel_vary_chpid_off,
NULL, &chpid); NULL, &chpid);