Changeset c170438 in mainline for uspace/lib/c/generic/async.c

Timestamp:

2016-05-24T21:00:37Z (9 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

2a7ba5e

Parents:

f570cdf

Message:

Do not create a new fibril for each IRQ notification

In the absence of fibril serialization, manager fibrils can
theoretically block in async IPC or on fibril synchronization
primitives. Consequently, it is safe to execute the IRQ handler directly
from the manager fibril. The manager fibril can block while processing
the notification, but most of the times it will not block and the
handler will execute atomically.

This changeset modifies the current behaviour so that we no longer spawn
a new notification fibril for each IRQ, but rather execute the handler
directly from the manager fibril and test if the execution blocked. If
it blocked, the manager fibril had assumed the role of a notification
fibril and we destroy it afterwards - merely to avoid fibril population
explosion. Otherwise, which is the usual behavior, we keep it so that
it resumes its job of a manager fibril.

File:

• uspace/lib/c/generic/async.c (modified) (5 diffs)

uspace/lib/c/generic/async.c

@@ -493 +493 @@
 }
 
-static size_t notification_handler_stksz = FIBRIL_DFLT_STK_SIZE;
-
-/** Set the stack size for the notification handler notification fibrils.
- *
- * @param size Stack size in bytes.
- */
-void async_set_notification_handler_stack_size(size_t size)
-{
-        notification_handler_stksz = size;
-}
-
 /** Mutex protecting inactive_exch_list and avail_phone_cv.
  *
@@ -998 +987 @@
 }
 
-/** Notification fibril.
- *
- * When a notification arrives, a fibril with this implementing function is
- * created. It calls the corresponding notification handler and does the final
- * cleanup.
- *
- * @param arg Message structure pointer.
- *
- * @return Always zero.
- *
- */
-static int notification_fibril(void *arg)
-{
-        assert(arg);
-        
-        msg_t *msg = (msg_t *) arg;
+/** Process notification.
+ *
+ * @param callid Hash of the incoming call.
+ * @param call   Data of the incoming call.
+ */
+static void process_notification(ipc_callid_t callid, ipc_call_t *call)
+{
         async_notification_handler_t handler = NULL;
         void *data = NULL;
+
+        assert(call);
         
         futex_down(&async_futex);
         
         ht_link_t *link = hash_table_find(&notification_hash_table,
-            &IPC_GET_IMETHOD(msg->call));
+            &IPC_GET_IMETHOD(*call));
         if (link) {
                 notification_t *notification =
@@ -1031 +1013 @@
         
         if (handler)
-                handler(msg->callid, &msg->call, data);
-        
-        free(msg);
-        return 0;
-}
-
-/** Process notification.
- *
- * A new fibril is created which would process the notification.
- *
- * @param callid Hash of the incoming call.
- * @param call   Data of the incoming call.
- *
- * @return False if an error occured.
- *         True if the call was passed to the notification fibril.
- *
- */
-static bool process_notification(ipc_callid_t callid, ipc_call_t *call)
-{
-        assert(call);
-        
-        futex_down(&async_futex);
-        
-        msg_t *msg = malloc(sizeof(*msg));
-        if (!msg) {
-                futex_up(&async_futex);
-                return false;
-        }
-        
-        msg->callid = callid;
-        msg->call = *call;
-        
-        fid_t fid = fibril_create_generic(notification_fibril, msg,
-            notification_handler_stksz);
-        if (fid == 0) {
-                free(msg);
-                futex_up(&async_futex);
-                return false;
-        }
-        
-        fibril_add_ready(fid);
-        
-        futex_up(&async_futex);
-        return true;
+                handler(callid, call, data);
 }
 
@@ -1375 +1314 @@
         /* Kernel notification */
         if ((callid & IPC_CALLID_NOTIFICATION)) {
+                fibril_t *fibril = (fibril_t *) __tcb_get()->fibril_data;
+                unsigned oldsw = fibril->switches;
+
                 process_notification(callid, call);
+
+                if (oldsw != fibril->switches) {
+                        /*
+                         * The notification handler did not execute atomically
+                         * and so the current manager fibril assumed the role of
+                         * a notification fibril. While waiting for its
+                         * resources, it switched to another manager fibril that
+                         * had already existed or it created a new one. We
+                         * therefore know there is at least yet another
+                         * manager fibril that can take over. We now kill the
+                         * current 'notification' fibril to prevent fibril
+                         * population explosion.
+                         */
+                        futex_down(&async_futex);
+                        fibril_switch(FIBRIL_FROM_DEAD);
+                }
                 return;
         }
@@ -1550 +1508 @@
 void async_create_manager(void)
 {
-        fid_t fid = fibril_create(async_manager_fibril, NULL);
+        fid_t fid = fibril_create_generic(async_manager_fibril, NULL, PAGE_SIZE);
         if (fid != 0)
                 fibril_add_manager(fid);