[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>

3 files changed, 137 insertions, 84 deletions

diff --git a/drivers/s390/cio/chsc.c b/drivers/s390/cio/chsc.c
index 12a344c66b46..93e6f74187ee 100644
--- a/drivers/s390/cio/chsc.c
+++ b/drivers/s390/cio/chsc.c
@@ -136,17 +136,13 @@ static void terminate_internal_io(struct subchannel *sch)
                 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 chpid)
 
         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 chsc_ssd_info *ssd,
         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_id schid, void *data)
                 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 res_acc_data *res_data)
          * 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 schid)
 }
 
 
-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;
-
-        chpid = data;
-        sch = get_subchannel_by_schid(schid);
-        if (!sch)
-                /* Check if the subchannel is now available. */
-                return __chp_add_new_sch(schid);
+        struct chp_id *chpid = data;
+
         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, void *data)
                 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(struct subchannel *sch,
         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, int on)
          * 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;
 }
 
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 69d56c7284d1..3b45bbe6cce0 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -51,6 +51,62 @@ for_each_subchannel(int(*fn)(struct subchannel_id, void *), void *data)
         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(void)
         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 subchannel_id schid, void *data)
         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_struct *unused)
         /* 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);
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);