Commit 70c60c08 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Kevin Wolf
Browse files

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: default avatarGabriel Kerneis <gabriel@kerneis.info>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarGabriel Kerneis <gabriel@kerneis.info>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 2c78857b

configure

+24 −0
Original line number Diff line number Diff line
@@ -238,6 +238,7 @@ win_sdk="no" 
want_tools="yes"

libiscsi=""

coroutine=""

coroutine_pool=""

seccomp=""

glusterfs=""

glusterfs_discard="no"
@@ -888,6 +889,10 @@ 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"
@@ -1189,6 +1194,8 @@ 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"
@@ -3362,6 +3369,17 @@ 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
@@ -3733,6 +3751,7 @@ echo "build guest agent $guest_agent" 
echo "QGA VSS support   $guest_agent_with_vss"

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              $gcov_tool"
@@ -4092,6 +4111,11 @@ if test "$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

qemu-coroutine.c

+19 −15
Original line number Diff line number Diff line
@@ -30,8 +30,9 @@ static unsigned int pool_size; 


Coroutine *qemu_coroutine_create(CoroutineEntry *entry)

{

    Coroutine *co;

    Coroutine *co = NULL;



    if (CONFIG_COROUTINE_POOL) {

        qemu_mutex_lock(&pool_lock);

        co = QSLIST_FIRST(&pool);

        if (co) {
@@ -39,6 +40,7 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry) 
            pool_size--;

        }

        qemu_mutex_unlock(&pool_lock);

    }



    if (!co) {

        co = qemu_coroutine_new();
@@ -51,6 +53,7 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry) 


static void coroutine_delete(Coroutine *co)

{

    if (CONFIG_COROUTINE_POOL) {

        qemu_mutex_lock(&pool_lock);

        if (pool_size < POOL_MAX_SIZE) {

            QSLIST_INSERT_HEAD(&pool, co, pool_next);
@@ -60,6 +63,7 @@ static void coroutine_delete(Coroutine *co) 
            return;

        }

        qemu_mutex_unlock(&pool_lock);

    }



    qemu_coroutine_delete(co);

}