The next patch will require the BQL to be always taken with
qemu_mutex_lock_iothread(), while right now this isn't the case.
Outside TCG mode this is not a problem. In TCG mode, we need to be
careful and avoid the "prod out of compiled code" step if already
in a VCPU thread. This is easily done with a check on current_cpu,
i.e. qemu_in_vcpu_thread().
Hopefully, multithreaded TCG will get rid of the whole logic to kick
VCPUs whenever an I/O event occurs!
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
cpus.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/cpus.c b/cpus.c
index de6469f..2e807f9 100644
--- a/cpus.c
+++ b/cpus.c
@@ -924,7 +924,7 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
CPUState *cpu = arg;
int r;
- qemu_mutex_lock(&qemu_global_mutex);
+ qemu_mutex_lock_iothread();
qemu_thread_get_self(cpu->thread);
cpu->thread_id = qemu_get_thread_id();
cpu->can_do_io = 1;
@@ -1004,10 +1004,10 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
{
CPUState *cpu = arg;
+ qemu_mutex_lock_iothread();
qemu_tcg_init_cpu_signals();
qemu_thread_get_self(cpu->thread);
- qemu_mutex_lock(&qemu_global_mutex);
CPU_FOREACH(cpu) {
cpu->thread_id = qemu_get_thread_id();
cpu->created = true;
@@ -1118,7 +1118,11 @@ bool qemu_in_vcpu_thread(void)
void qemu_mutex_lock_iothread(void)
{
atomic_inc(&iothread_requesting_mutex);
- if (!tcg_enabled() || !first_cpu || !first_cpu->thread) {
+ /* In the simple case there is no need to bump the VCPU thread out of
+ * TCG code execution.
+ */
+ if (!tcg_enabled() || qemu_in_vcpu_thread() ||
+ !first_cpu || !first_cpu->thread) {
qemu_mutex_lock(&qemu_global_mutex);
atomic_dec(&iothread_requesting_mutex);
} else {
--
1.8.3.1
