Re: [PULL 22/33] migration: remove the QEMUFileOps 'get_buffer' callback

[Peter Xu]

On Mon, Jun 27, 2022 at 04:03:09PM +0100, Daniel P. Berrangé wrote:
> On Wed, Jun 22, 2022 at 03:34:52PM -0400, Peter Xu wrote:
> > On Wed, Jun 22, 2022 at 07:39:06PM +0100, Dr. David Alan Gilbert (git) 
> > wrote:
> > > diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> > > index 74f919de67..e206b05550 100644
> > > --- a/migration/qemu-file.c
> > > +++ b/migration/qemu-file.c
> > > @@ -377,8 +377,22 @@ static ssize_t qemu_fill_buffer(QEMUFile *f)
> > >          return 0;
> > >      }
> > >  
> > > -    len = f->ops->get_buffer(f->ioc, f->buf + pending, 
> > > f->total_transferred,
> > > -                             IO_BUF_SIZE - pending, &local_error);
> > > +    do {
> > > +        len = qio_channel_read(f->ioc,
> > > +                               (char *)f->buf + pending,
> > > +                               IO_BUF_SIZE - pending,
> > > +                               &local_error);
> > > +        if (len == QIO_CHANNEL_ERR_BLOCK) {
> > > +            if (qemu_in_coroutine()) {
> > > +                qio_channel_yield(f->ioc, G_IO_IN);
> > > +            } else {
> > > +                qio_channel_wait(f->ioc, G_IO_IN);
> > > +            }
> > > +        } else if (len < 0) {
> > > +            len = EIO;
> > 
> > This should be -EIO.
> > 
> > > +        }
> > > +    } while (len == QIO_CHANNEL_ERR_BLOCK);
> > 
> > It's failing only with the new TLS test I added for postcopy somehow (at
> > least /x86_64/migration/postcopy/recovery/tls).. I also verified after the
> > change it'll work again.
> 
> Assuming you can still reproduce the pre-existing flaw, can you capture
> a stack trace when it hangs.   I'm wondering if it is a sign that the
> migration is not converging when using TLS under certain load conditions,
> because the test waits forever for converge.

Yes it is, and it reproduces here every time.  It hangs at:

 if (!got_stop) {
     qtest_qmp_eventwait(from, "STOP");
 }

> 
> Also what scenario are you running in ? Bare metal or a VM, and what
> host arch ? Wondering if the machine is at all slow, or for example
> missing AES hardware acceleration or some such thing.

It's Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz, 40 cores.

It'll pass after I modify the downtime:

  migrate_set_parameter_int(from, "downtime-limit", 100000);

And with QTEST_LOG=1 I found that the bw is indeed low, ~700mbps.

-- 
Peter Xu