From b84c4586234b26ccc875595713f6f4491e5b3385 Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Fri, 17 May 2013 15:51:25 +0200
Subject: coroutine: protect global pool with a mutex

The coroutine freelist is a global pool of unused coroutines.  It avoids
the setup/teardown overhead associated with the coroutine lifecycle.
Since the pool is global, we need to synchronize access so that
coroutines can be used outside the BQL.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 qemu-coroutine.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

(limited to 'qemu-coroutine.c')

diff --git a/qemu-coroutine.c b/qemu-coroutine.c
index 25a14c6..60ac79e 100644
--- a/qemu-coroutine.c
+++ b/qemu-coroutine.c
@@ -14,6 +14,7 @@
 
 #include "trace.h"
 #include "qemu-common.h"
+#include "qemu/thread.h"
 #include "block/coroutine.h"
 #include "block/coroutine_int.h"
 
@@ -23,6 +24,7 @@ enum {
 };
 
 /** Free list to speed up creation */
+static QemuMutex pool_lock;
 static QSLIST_HEAD(, Coroutine) pool = QSLIST_HEAD_INITIALIZER(pool);
 static unsigned int pool_size;
 
@@ -30,11 +32,15 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
 {
     Coroutine *co;
 
+    qemu_mutex_lock(&pool_lock);
     co = QSLIST_FIRST(&pool);
     if (co) {
         QSLIST_REMOVE_HEAD(&pool, pool_next);
         pool_size--;
-    } else {
+    }
+    qemu_mutex_unlock(&pool_lock);
+
+    if (!co) {
         co = qemu_coroutine_new();
     }
 
@@ -44,17 +50,25 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
 
 static void coroutine_delete(Coroutine *co)
 {
+    qemu_mutex_lock(&pool_lock);
     if (pool_size < POOL_MAX_SIZE) {
         QSLIST_INSERT_HEAD(&pool, co, pool_next);
         co->caller = NULL;
         pool_size++;
+        qemu_mutex_unlock(&pool_lock);
         return;
     }
+    qemu_mutex_unlock(&pool_lock);
 
     qemu_coroutine_delete(co);
 }
 
-static void __attribute__((destructor)) coroutine_cleanup(void)
+static void __attribute__((constructor)) coroutine_pool_init(void)
+{
+    qemu_mutex_init(&pool_lock);
+}
+
+static void __attribute__((destructor)) coroutine_pool_cleanup(void)
 {
     Coroutine *co;
     Coroutine *tmp;
@@ -63,6 +77,8 @@ static void __attribute__((destructor)) coroutine_cleanup(void)
         QSLIST_REMOVE_HEAD(&pool, pool_next);
         qemu_coroutine_delete(co);
     }
+
+    qemu_mutex_destroy(&pool_lock);
 }
 
 static void coroutine_swap(Coroutine *from, Coroutine *to)
-- 
cgit v1.1


From 02ffb504485f0920cfc75a0982a602f824a9a4f4 Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Fri, 17 May 2013 15:51:26 +0200
Subject: coroutine: stop using AioContext in CoQueue

qemu_co_queue_next(&queue) arranges that the next queued coroutine is
run at a later point in time.  This deferred restart is useful because
the caller may not want to transfer control yet.

This behavior was implemented using QEMUBH in the past, which meant that
CoQueue (and hence CoMutex and CoRwlock) had a dependency on the
AioContext event loop.  This hidden dependency causes trouble when we
move to a world with multiple event loops - now qemu_co_queue_next()
needs to know which event loop to schedule the QEMUBH in.

After pondering how to stash AioContext I realized the best solution is
to not use AioContext at all.  This patch implements the deferred
restart behavior purely in terms of coroutines and no longer uses
QEMUBH.

Here is how it works:

Each Coroutine has a wakeup queue that starts out empty.  When
qemu_co_queue_next() is called, the next coroutine is added to our
wakeup queue.  The wakeup queue is processed when we yield or terminate.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 qemu-coroutine.c | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'qemu-coroutine.c')

diff --git a/qemu-coroutine.c b/qemu-coroutine.c
index 60ac79e..423430d 100644
--- a/qemu-coroutine.c
+++ b/qemu-coroutine.c
@@ -45,6 +45,7 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
     }
 
     co->entry = entry;
+    QTAILQ_INIT(&co->co_queue_wakeup);
     return co;
 }
 
@@ -87,6 +88,8 @@ static void coroutine_swap(Coroutine *from, Coroutine *to)
 
     ret = qemu_coroutine_switch(from, to, COROUTINE_YIELD);
 
+    qemu_co_queue_run_restart(to);
+
     switch (ret) {
     case COROUTINE_YIELD:
         return;
-- 
cgit v1.1