[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, 102 insertions, 18 deletions

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);