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Subject[patch 13/47] cio: reduce cpu utilization during device scan
From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>

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>
---
drivers/s390/cio/chsc.c | 96 ++++++++++++--------------------------
drivers/s390/cio/css.c | 120 ++++++++++++++++++++++++++++++++++++++++--------
drivers/s390/cio/css.h | 3 +
3 files changed, 136 insertions(+), 83 deletions(-)
Index: quilt-2.6/drivers/s390/cio/chsc.c
===================================================================
--- quilt-2.6.orig/drivers/s390/cio/chsc.c
+++ quilt-2.6/drivers/s390/cio/chsc.c
@@ -136,17 +136,13 @@ static void terminate_internal_io(struct
sch->driver->termination(sch);
}

-static int
-s390_subchannel_remove_chpid(struct device *dev, void *data)
+static int s390_subchannel_remove_chpid(struct subchannel *sch, void *data)
{
int j;
int mask;
- struct subchannel *sch;
- struct chp_id *chpid;
+ struct chp_id *chpid = data;
struct schib schib;

- sch = to_subchannel(dev);
- chpid = data;
for (j = 0; j < 8; j++) {
mask = 0x80 >> j;
if ((sch->schib.pmcw.pim & mask) &&
@@ -202,12 +198,10 @@ void chsc_chp_offline(struct chp_id chpi

if (chp_get_status(chpid) <= 0)
return;
- bus_for_each_dev(&css_bus_type, NULL, &chpid,
- s390_subchannel_remove_chpid);
+ for_each_subchannel_staged(s390_subchannel_remove_chpid, NULL, &chpid);
}

-static int
-s390_process_res_acc_new_sch(struct subchannel_id schid)
+static int s390_process_res_acc_new_sch(struct subchannel_id schid, void *data)
{
struct schib schib;
/*
@@ -253,18 +247,10 @@ static int get_res_chpid_mask(struct chs
return 0;
}

-static int
-__s390_process_res_acc(struct subchannel_id schid, void *data)
+static int __s390_process_res_acc(struct subchannel *sch, void *data)
{
int chp_mask, old_lpm;
- struct res_acc_data *res_data;
- struct subchannel *sch;
-
- res_data = data;
- sch = get_subchannel_by_schid(schid);
- if (!sch)
- /* Check if a subchannel is newly available. */
- return s390_process_res_acc_new_sch(schid);
+ struct res_acc_data *res_data = data;

spin_lock_irq(sch->lock);
chp_mask = get_res_chpid_mask(&sch->ssd_info, res_data);
@@ -283,7 +269,7 @@ __s390_process_res_acc(struct subchannel
sch->driver->verify(sch);
out:
spin_unlock_irq(sch->lock);
- put_device(&sch->dev);
+
return 0;
}

@@ -306,7 +292,8 @@ static void s390_process_res_acc (struct
* The more information we have (info), the less scanning
* will we have to do.
*/
- for_each_subchannel(__s390_process_res_acc, res_data);
+ for_each_subchannel_staged(__s390_process_res_acc,
+ s390_process_res_acc_new_sch, res_data);
}

static int
@@ -500,8 +487,7 @@ void chsc_process_crw(void)
} while (sei_area->flags & 0x80);
}

-static int
-__chp_add_new_sch(struct subchannel_id schid)
+static int __chp_add_new_sch(struct subchannel_id schid, void *data)
{
struct schib schib;

@@ -515,35 +501,27 @@ __chp_add_new_sch(struct subchannel_id s
}


-static int
-__chp_add(struct subchannel_id schid, void *data)
+static int __chp_add(struct subchannel *sch, void *data)
{
int i, mask;
- struct chp_id *chpid;
- struct subchannel *sch;
+ struct chp_id *chpid = data;

- chpid = data;
- sch = get_subchannel_by_schid(schid);
- if (!sch)
- /* Check if the subchannel is now available. */
- return __chp_add_new_sch(schid);
spin_lock_irq(sch->lock);
for (i=0; i<8; i++) {
mask = 0x80 >> i;
if ((sch->schib.pmcw.pim & mask) &&
- (sch->schib.pmcw.chpid[i] == chpid->id)) {
- if (stsch(sch->schid, &sch->schib) != 0) {
- /* Endgame. */
- spin_unlock_irq(sch->lock);
- return -ENXIO;
- }
+ (sch->schib.pmcw.chpid[i] == chpid->id))
break;
- }
}
if (i==8) {
spin_unlock_irq(sch->lock);
return 0;
}
+ if (stsch(sch->schid, &sch->schib)) {
+ spin_unlock_irq(sch->lock);
+ css_schedule_eval(sch->schid);
+ return 0;
+ }
sch->lpm = ((sch->schib.pmcw.pim &
sch->schib.pmcw.pam &
sch->schib.pmcw.pom)
@@ -553,7 +531,7 @@ __chp_add(struct subchannel_id schid, vo
sch->driver->verify(sch);

spin_unlock_irq(sch->lock);
- put_device(&sch->dev);
+
return 0;
}

@@ -565,7 +543,8 @@ void chsc_chp_online(struct chp_id chpid
CIO_TRACE_EVENT(2, dbf_txt);

if (chp_get_status(chpid) != 0)
- for_each_subchannel(__chp_add, &chpid);
+ for_each_subchannel_staged(__chp_add, __chp_add_new_sch,
+ &chpid);
}

static void __s390_subchannel_vary_chpid(struct subchannel *sch,
@@ -616,25 +595,17 @@ static void __s390_subchannel_vary_chpid
spin_unlock_irqrestore(sch->lock, flags);
}

-static int s390_subchannel_vary_chpid_off(struct device *dev, void *data)
+static int s390_subchannel_vary_chpid_off(struct subchannel *sch, void *data)
{
- struct subchannel *sch;
- struct chp_id *chpid;
-
- sch = to_subchannel(dev);
- chpid = data;
+ struct chp_id *chpid = data;

__s390_subchannel_vary_chpid(sch, *chpid, 0);
return 0;
}

-static int s390_subchannel_vary_chpid_on(struct device *dev, void *data)
+static int s390_subchannel_vary_chpid_on(struct subchannel *sch, void *data)
{
- struct subchannel *sch;
- struct chp_id *chpid;
-
- sch = to_subchannel(dev);
- chpid = data;
+ struct chp_id *chpid = data;

__s390_subchannel_vary_chpid(sch, *chpid, 1);
return 0;
@@ -644,13 +615,7 @@ static int
__s390_vary_chpid_on(struct subchannel_id schid, void *data)
{
struct schib schib;
- struct subchannel *sch;

- sch = get_subchannel_by_schid(schid);
- if (sch) {
- put_device(&sch->dev);
- return 0;
- }
if (stsch_err(schid, &schib))
/* We're through */
return -ENXIO;
@@ -670,12 +635,13 @@ int chsc_chp_vary(struct chp_id chpid, i
* Redo PathVerification on the devices the chpid connects to
*/

- bus_for_each_dev(&css_bus_type, NULL, &chpid, on ?
- s390_subchannel_vary_chpid_on :
- s390_subchannel_vary_chpid_off);
if (on)
- /* Scan for new devices on varied on path. */
- for_each_subchannel(__s390_vary_chpid_on, NULL);
+ for_each_subchannel_staged(s390_subchannel_vary_chpid_on,
+ __s390_vary_chpid_on, &chpid);
+ else
+ for_each_subchannel_staged(s390_subchannel_vary_chpid_off,
+ NULL, &chpid);
+
return 0;
}

Index: quilt-2.6/drivers/s390/cio/css.c
===================================================================
--- quilt-2.6.orig/drivers/s390/cio/css.c
+++ quilt-2.6/drivers/s390/cio/css.c
@@ -51,6 +51,62 @@ for_each_subchannel(int(*fn)(struct subc
return ret;
}

+struct cb_data {
+ void *data;
+ struct idset *set;
+ int (*fn_known_sch)(struct subchannel *, void *);
+ int (*fn_unknown_sch)(struct subchannel_id, void *);
+};
+
+static int call_fn_known_sch(struct device *dev, void *data)
+{
+ struct subchannel *sch = to_subchannel(dev);
+ struct cb_data *cb = data;
+ int rc = 0;
+
+ idset_sch_del(cb->set, sch->schid);
+ if (cb->fn_known_sch)
+ rc = cb->fn_known_sch(sch, cb->data);
+ return rc;
+}
+
+static int call_fn_unknown_sch(struct subchannel_id schid, void *data)
+{
+ struct cb_data *cb = data;
+ int rc = 0;
+
+ if (idset_sch_contains(cb->set, schid))
+ rc = cb->fn_unknown_sch(schid, cb->data);
+ return rc;
+}
+
+int for_each_subchannel_staged(int (*fn_known)(struct subchannel *, void *),
+ int (*fn_unknown)(struct subchannel_id,
+ void *), void *data)
+{
+ struct cb_data cb;
+ int rc;
+
+ cb.set = idset_sch_new();
+ if (!cb.set)
+ return -ENOMEM;
+ idset_fill(cb.set);
+ cb.data = data;
+ cb.fn_known_sch = fn_known;
+ cb.fn_unknown_sch = fn_unknown;
+ /* Process registered subchannels. */
+ rc = bus_for_each_dev(&css_bus_type, NULL, &cb, call_fn_known_sch);
+ if (rc)
+ goto out;
+ /* Process unregistered subchannels. */
+ if (fn_unknown)
+ rc = for_each_subchannel(call_fn_unknown_sch, &cb);
+out:
+ idset_free(cb.set);
+
+ return rc;
+}
+
static struct subchannel *
css_alloc_subchannel(struct subchannel_id schid)
{
@@ -402,20 +458,56 @@ static int __init slow_subchannel_init(v
return 0;
}

-static void css_slow_path_func(struct work_struct *unused)
+static int slow_eval_known_fn(struct subchannel *sch, void *data)
{
- struct subchannel_id schid;
+ int eval;
+ int rc;

- CIO_TRACE_EVENT(4, "slowpath");
spin_lock_irq(&slow_subchannel_lock);
- init_subchannel_id(&schid);
- while (idset_sch_get_first(slow_subchannel_set, &schid)) {
- idset_sch_del(slow_subchannel_set, schid);
- spin_unlock_irq(&slow_subchannel_lock);
- css_evaluate_subchannel(schid, 1);
- spin_lock_irq(&slow_subchannel_lock);
+ eval = idset_sch_contains(slow_subchannel_set, sch->schid);
+ idset_sch_del(slow_subchannel_set, sch->schid);
+ spin_unlock_irq(&slow_subchannel_lock);
+ if (eval) {
+ rc = css_evaluate_known_subchannel(sch, 1);
+ if (rc == -EAGAIN)
+ css_schedule_eval(sch->schid);
}
+ return 0;
+}
+
+static int slow_eval_unknown_fn(struct subchannel_id schid, void *data)
+{
+ int eval;
+ int rc = 0;
+
+ spin_lock_irq(&slow_subchannel_lock);
+ eval = idset_sch_contains(slow_subchannel_set, schid);
+ idset_sch_del(slow_subchannel_set, schid);
spin_unlock_irq(&slow_subchannel_lock);
+ if (eval) {
+ rc = css_evaluate_new_subchannel(schid, 1);
+ switch (rc) {
+ case -EAGAIN:
+ css_schedule_eval(schid);
+ rc = 0;
+ break;
+ case -ENXIO:
+ case -ENOMEM:
+ case -EIO:
+ /* These should abort looping */
+ break;
+ default:
+ rc = 0;
+ }
+ }
+ return rc;
+}
+
+static void css_slow_path_func(struct work_struct *unused)
+{
+ CIO_TRACE_EVENT(4, "slowpath");
+ for_each_subchannel_staged(slow_eval_known_fn, slow_eval_unknown_fn,
+ NULL);
}

static DECLARE_WORK(slow_path_work, css_slow_path_func);
@@ -444,7 +536,6 @@ void css_schedule_eval_all(void)
/* Reprobe subchannel if unregistered. */
static int reprobe_subchannel(struct subchannel_id schid, void *data)
{
- struct subchannel *sch;
int ret;

CIO_MSG_EVENT(6, "cio: reprobe 0.%x.%04x\n",
@@ -452,13 +543,6 @@ static int reprobe_subchannel(struct sub
if (need_reprobe)
return -EAGAIN;

- sch = get_subchannel_by_schid(schid);
- if (sch) {
- /* Already known. */
- put_device(&sch->dev);
- return 0;
- }
-
ret = css_probe_device(schid);
switch (ret) {
case 0:
@@ -486,7 +570,7 @@ static void reprobe_all(struct work_stru
/* Make sure initial subchannel scan is done. */
wait_event(ccw_device_init_wq,
atomic_read(&ccw_device_init_count) == 0);
- ret = for_each_subchannel(reprobe_subchannel, NULL);
+ ret = for_each_subchannel_staged(NULL, reprobe_subchannel, NULL);

CIO_MSG_EVENT(2, "reprobe done (rc=%d, need_reprobe=%d)\n", ret,
need_reprobe);
Index: quilt-2.6/drivers/s390/cio/css.h
===================================================================
--- quilt-2.6.orig/drivers/s390/cio/css.h
+++ quilt-2.6/drivers/s390/cio/css.h
@@ -91,6 +91,9 @@ extern void css_driver_unregister(struct
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);
--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.



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