On Wed, Dec 08, 2021 at 07:46:20PM +0000, Dr. David Alan Gilbert wrote:
> * Peter Xu (pet...@redhat.com) wrote:
> > The enablement of postcopy listening has a few steps, add a few tracepoints
> > to
> > be there ready for some basic measurements for them.
> >
> > Signed-off-by: Peter Xu <pet...@redhat.com>
> > ---
> > migration/savevm.c | 5 ++++-
> > migration/trace-events | 2 +-
> > 2 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index 17b8e25e00..5b3f31eab2 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -1946,7 +1946,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
> > static int loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
> > {
> > PostcopyState ps = postcopy_state_set(POSTCOPY_INCOMING_LISTENING);
> > - trace_loadvm_postcopy_handle_listen();
> > + trace_loadvm_postcopy_handle_listen(1);
>
> I think we tend just to split this into separate traces in many places;
> or if we're using the same one then we should use a string
>
> I'd make this:
> trace_loadvm_postcopy_handle_listen_entry();
>
> for example.
>
> > Error *local_err = NULL;
> >
> > if (ps != POSTCOPY_INCOMING_ADVISE && ps != POSTCOPY_INCOMING_DISCARD)
> > {
> > @@ -1962,6 +1962,7 @@ static int
> > loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
> > postcopy_ram_prepare_discard(mis);
> > }
> > }
> > + trace_loadvm_postcopy_handle_listen(2);
> >
> > /*
> > * Sensitise RAM - can now generate requests for blocks that don't
> > exist
> > @@ -1974,6 +1975,7 @@ static int
> > loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
> > return -1;
> > }
> > }
> > + trace_loadvm_postcopy_handle_listen(3);
> >
> > if (postcopy_notify(POSTCOPY_NOTIFY_INBOUND_LISTEN, &local_err)) {
> > error_report_err(local_err);
> > @@ -1988,6 +1990,7 @@ static int
> > loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
> > QEMU_THREAD_DETACHED);
> > qemu_sem_wait(&mis->listen_thread_sem);
> > qemu_sem_destroy(&mis->listen_thread_sem);
> > + trace_loadvm_postcopy_handle_listen(4);
>
> trace_loadvm_postcopy_handle_listen_entry_end();
I see, I can use it. It's just that I want to trap more than entry/exit.
For the "4 steps" here I split it into four procedures, the 2 steps inside are
majorly to trap either uffd registration time or external uffd handling of
other processes.
One example:
We may want to know how slow is postcopy_notify(POSTCOPY_NOTIFY_INBOUND_LISTEN)
when there're some external process attached. I wanted to be prepared for that
so when there's need to evaluate slowness of this procedure with vhost-user
enabled we have some tracepoints without replacing the binaries.
It's easy to use strings too if that's better looking than numbers. How about:
trace_loadvm_postcopy_handle_listen("entry")
trace_loadvm_postcopy_handle_listen("uffd-reg")
trace_loadvm_postcopy_handle_listen("external")
trace_loadvm_postcopy_handle_listen("exit")
?
Thanks,
--
Peter Xu
