On Fri, Sep 22, 2023 at 01:06:53PM -0300, Fabiano Rosas wrote:
> Elena Ufimtseva <elena.ufimts...@oracle.com> writes:
>
> > In multifd_send_sync_main we need to wait for channels_ready
> > before submitting sync packet as the threads may still be sending
> > their previous pages.
> > There is also no need to check for channels_ready in the loop
> > before the wait for sem_sync, next iteration of sending pages
> > or another sync will start with waiting for channels_ready
> > semaphore.
> > Changes to commit 90b3cec351996dd8ef4eb847ad38607812c5e7f5
> > ("multifd: Fix the number of channels ready")
> >
> > Signed-off-by: Elena Ufimtseva <elena.ufimts...@oracle.com>
> > ---
> > migration/multifd.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/migration/multifd.c b/migration/multifd.c
> > index 0f6b203877..e61e458151 100644
> > --- a/migration/multifd.c
> > +++ b/migration/multifd.c
> > @@ -595,6 +595,7 @@ int multifd_send_sync_main(QEMUFile *f)
> > }
> > }
> >
> > + qemu_sem_wait(&multifd_send_state->channels_ready);
> > /*
> > * When using zero-copy, it's necessary to flush the pages before any
> > of
> > * the pages can be sent again, so we'll make sure the new version of
> > the
> > @@ -630,7 +631,6 @@ 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);
>
> Please take a look at the series I just sent. Basically, I think we
> should wait on 'sem' for the number of existing channels and not just
> once per sync. Otherwise I think we'd hit the same issue this patch is
> trying to fix when we loop into the n+1 channels. I think the
> assert(!p->pending_job) in patch 3 helps prove that's more appropriate.
Thank you!
These patches make sense to me.
Agree on redundant sem_sync. Lets see what others think.
I will run some tests as well with your patches and spend
more time looking at [2/3] patch.
Elena U.
>
> Let me know what you think.
>
> Thanks
