From ba20326a937421c50a775907dc9ac726bb9a9b50 Mon Sep 17 00:00:00 2001

From: Stefan Hajnoczi <stefanha@redhat.com>

Date: Wed, 11 Sep 2013 16:42:35 +0200

Subject: [PATCH] coroutine: add ./configure --disable-coroutine-pool

The 'gthread' coroutine backend was written before the freelist (aka

pool) existed in qemu-coroutine.c.

This means that every thread is expected to exit when its coroutine

terminates.  It is not possible to reuse threads from a pool.

This patch automatically disables the pool when 'gthread' is used.  This

allows the 'gthread' backend to work again (for example,

tests/test-coroutine completes successfully instead of hanging).

I considered implementing thread reuse but I don't want quirks like CPU

affinity differences due to coroutine threads being recycled.  The

'gthread' backend is a reference backend and it's therefore okay to skip

the pool optimization.

Note this patch also makes it easy to toggle the pool for benchmarking

purposes:

  ./configure --with-coroutine-backend=ucontext \

              --disable-coroutine-pool

Reported-by: Gabriel Kerneis <gabriel@kerneis.info>

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Gabriel Kerneis <gabriel@kerneis.info>

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

(cherry picked from commit 70c60c089fdc6bf8a79324e492c13e8c08d55942)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

---

 configure        | 24 ++++++++++++++++++++++++

 qemu-coroutine.c | 34 +++++++++++++++++++---------------

 2 files changed, 43 insertions(+), 15 deletions(-)

diff --git a/configure b/configure

index 18fa608..4cf672d 100755

--- a/configure

+++ b/configure

@@ -235,6 +235,7 @@ guest_agent=""

 want_tools="yes"

 libiscsi=""

 coroutine=""

+coroutine_pool=""

 seccomp=""

 glusterfs=""

 glusterfs_discard="no"

@@ -871,6 +872,10 @@ for opt do

   ;;

   --with-coroutine=*) coroutine="$optarg"

   ;;

+  --disable-coroutine-pool) coroutine_pool="no"

+  ;;

+  --enable-coroutine-pool) coroutine_pool="yes"

+  ;;

   --disable-docs) docs="no"

   ;;

   --enable-docs) docs="yes"

@@ -1152,6 +1157,8 @@ echo "  --disable-seccomp        disable seccomp support"

 echo "  --enable-seccomp         enables seccomp support"

 echo "  --with-coroutine=BACKEND coroutine backend. Supported options:"

 echo "                           gthread, ucontext, sigaltstack, windows"

+echo "  --disable-coroutine-pool disable coroutine freelist (worse performance)"

+echo "  --enable-coroutine-pool  enable coroutine freelist (better performance)"

 echo "  --enable-glusterfs       enable GlusterFS backend"

 echo "  --disable-glusterfs      disable GlusterFS backend"

 echo "  --enable-gcov            enable test coverage analysis with gcov"

@@ -3240,6 +3247,17 @@ else

   esac

 fi

+if test "$coroutine_pool" = ""; then

+  if test "$coroutine" = "gthread"; then

+    coroutine_pool=no

+  else

+    coroutine_pool=yes

+  fi

+fi

+if test "$coroutine" = "gthread" -a "$coroutine_pool" = "yes"; then

+  error_exit "'gthread' coroutine backend does not support pool (use --disable-coroutine-pool)"

+fi

+

 ##########################################

 # check if we have open_by_handle_at

@@ -3605,6 +3623,7 @@ echo "libiscsi support  $libiscsi"

 echo "build guest agent $guest_agent"

 echo "seccomp support   $seccomp"

 echo "coroutine backend $coroutine"

+echo "coroutine pool    $coroutine_pool"

 echo "GlusterFS support $glusterfs"

 echo "virtio-blk-data-plane $virtio_blk_data_plane"

 echo "gcov              $gcov_tool"

@@ -3954,6 +3973,11 @@ if test "$rbd" = "yes" ; then

 fi

 echo "CONFIG_COROUTINE_BACKEND=$coroutine" >> $config_host_mak

+if test "$coroutine_pool" = "yes" ; then

+  echo "CONFIG_COROUTINE_POOL=1" >> $config_host_mak

+else

+  echo "CONFIG_COROUTINE_POOL=0" >> $config_host_mak

+fi

 if test "$open_by_handle_at" = "yes" ; then

   echo "CONFIG_OPEN_BY_HANDLE=y" >> $config_host_mak

diff --git a/qemu-coroutine.c b/qemu-coroutine.c

index 423430d..4708521 100644

--- a/qemu-coroutine.c

+++ b/qemu-coroutine.c

@@ -30,15 +30,17 @@ static unsigned int pool_size;

 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--;

+    Coroutine *co = NULL;

+

+    if (CONFIG_COROUTINE_POOL) {

+        qemu_mutex_lock(&pool_lock);

+        co = QSLIST_FIRST(&pool);

+        if (co) {

+            QSLIST_REMOVE_HEAD(&pool, pool_next);

+            pool_size--;

+        }

+        qemu_mutex_unlock(&pool_lock);

     }

-    qemu_mutex_unlock(&pool_lock);

     if (!co) {

         co = qemu_coroutine_new();

@@ -51,15 +53,17 @@ 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++;

+    if (CONFIG_COROUTINE_POOL) {

+        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);

-        return;

     }

-    qemu_mutex_unlock(&pool_lock);

     qemu_coroutine_delete(co);

 }