We don't wait in the sem when we are doing a sync_main.  Make it wait
there.  To make things clearer, we mark the channel ready at the
begining of the thread loop.

Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 migration/multifd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index 903df2117b..e625e8725e 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -635,6 +635,7 @@ int multifd_send_sync_main(QEMUFile *f)
     for (i = 0; i < migrate_multifd_channels(); i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
 
+        qemu_sem_wait(&multifd_send_state->channels_ready);
         trace_multifd_send_sync_main_wait(p->id);
         qemu_sem_wait(&p->sem_sync);
 
@@ -668,6 +669,7 @@ static void *multifd_send_thread(void *opaque)
     p->num_packets = 1;
 
     while (true) {
+        qemu_sem_post(&multifd_send_state->channels_ready);
         qemu_sem_wait(&p->sem);
 
         if (qatomic_read(&multifd_send_state->exiting)) {
@@ -736,7 +738,6 @@ static void *multifd_send_thread(void *opaque)
             if (flags & MULTIFD_FLAG_SYNC) {
                 qemu_sem_post(&p->sem_sync);
             }
-            qemu_sem_post(&multifd_send_state->channels_ready);
         } else if (p->quit) {
             qemu_mutex_unlock(&p->mutex);
             break;
-- 
2.40.0

Juan Quintela <quintela@redhat.com> writes:

> We don't wait in the sem when we are doing a sync_main.  Make it wait
> there.  To make things clearer, we mark the channel ready at the
> begining of the thread loop.
>
> Signed-off-by: Juan Quintela <quintela@redhat.com>

Reviewed-by: Fabiano Rosas <farosas@suse.de>

Juan Quintela <quintela@redhat.com> writes:

> We don't wait in the sem when we are doing a sync_main.  Make it wait
> there.  To make things clearer, we mark the channel ready at the
> begining of the thread loop.

So in other words we're estabilishing that "channel ready" means ready
to send, regardless of having sent the sync packet. Is that it?

Fabiano Rosas <farosas@suse.de> wrote:
> Juan Quintela <quintela@redhat.com> writes:
>
>> We don't wait in the sem when we are doing a sync_main.  Make it wait
>> there.  To make things clearer, we mark the channel ready at the
>> begining of the thread loop.
>
> So in other words we're estabilishing that "channel ready" means ready
> to send, regardless of having sent the sync packet. Is that it?

Yeap.

There was a bug (from the beggining) that made the counter always get
up and up.  This fixes it.

It was always supposed to work this way.

/me puts (second time in the week) a brown paper bag on head

Later, Juan.

Juan Quintela <quintela@redhat.com> writes:

> Fabiano Rosas <farosas@suse.de> wrote:
>> Juan Quintela <quintela@redhat.com> writes:
>>
>>> We don't wait in the sem when we are doing a sync_main.  Make it wait
>>> there.  To make things clearer, we mark the channel ready at the
>>> begining of the thread loop.
>>
>> So in other words we're estabilishing that "channel ready" means ready
>> to send, regardless of having sent the sync packet. Is that it?
>
> Yeap.
>
> There was a bug (from the beggining) that made the counter always get
> up and up.  This fixes it.
>
> It was always supposed to work this way.

Ah, great. I'm proposing a multifd variant without the sync packet in my
fixed-ram series and moving the channels_ready to the top of the loop
means I can stop issuing an extra qemu_sem_post(&p->sem) just to skip
the sync packet.