Re: [Qemu-devel] [PULL 30/30] vl: smp_parse: cleanups

[Andrew Jones <drjones@redhat.com>]

On Tue, Jun 21, 2016 at 05:40:13PM +0200, Igor Mammedov wrote:
> On Thu, 16 Jun 2016 16:16:25 +0200
> Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> > From: Andrew Jones <drjones@redhat.com>
> > 
> > No functional changes; only some code movement and removal of
> > dead code (impossible conditions). Also, max_cpus can be
> > initialized to 1, like smp_cpus, because it's either set by the
> > user or set to smp_cpus, when smp_cpus is set by the user, or
> > set to 1, when nothing is set.
> > 
> > Signed-off-by: Andrew Jones <drjones@redhat.com>
> > Message-Id: <1465580427-13596-2-git-send-email-drjones@redhat.com>
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> this patch broke master with following CLI
>   -machine q35,accel=tcg -smp 2,cores=3,sockets=2,maxcpus=6

I see why. The "real" problem is the whole using 'cpus' instead of
'maxcpus' again, but, since that ship sailed, I guess I should be
careful with calculations like

 threads = cpus / (cores * sockets)

which can result in zero.

I'll send a patch right now.

Thanks,
drew

> 
> 
> 
> > ---
> >  vl.c | 34 +++++++++++++++-------------------
> >  1 file changed, 15 insertions(+), 19 deletions(-)
> > 
> > diff --git a/vl.c b/vl.c
> > index 99c3030..e69ebfd 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -154,7 +154,7 @@ CharDriverState *sclp_hds[MAX_SCLP_CONSOLES];
> >  int win2k_install_hack = 0;
> >  int singlestep = 0;
> >  int smp_cpus = 1;
> > -int max_cpus = 0;
> > +int max_cpus = 1;
> >  int smp_cores = 1;
> >  int smp_threads = 1;
> >  int acpi_enabled = 1;
> > @@ -1223,7 +1223,6 @@ static QemuOptsList qemu_smp_opts = {
> >  static void smp_parse(QemuOpts *opts)
> >  {
> >      if (opts) {
> > -
> >          unsigned cpus    = qemu_opt_get_number(opts, "cpus", 0);
> >          unsigned sockets = qemu_opt_get_number(opts, "sockets", 0);
> >          unsigned cores   = qemu_opt_get_number(opts, "cores", 0);
> > @@ -1251,6 +1250,17 @@ static void smp_parse(QemuOpts *opts)
> >          }
> >  
> >          max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
> > +
> > +        if (max_cpus > MAX_CPUMASK_BITS) {
> > +            error_report("unsupported number of maxcpus");
> > +            exit(1);
> > +        }
> > +
> > +        if (max_cpus < cpus) {
> > +            error_report("maxcpus must be equal to or greater than
> > smp");
> > +            exit(1);
> > +        }
> > +
> >          if (sockets * cores * threads > max_cpus) {
> >              error_report("cpu topology: "
> >                           "sockets (%u) * cores (%u) * threads (%u) >
> > " @@ -1260,25 +1270,11 @@ static void smp_parse(QemuOpts *opts)
> >          }
> >  
> >          smp_cpus = cpus;
> > -        smp_cores = cores > 0 ? cores : 1;
> > -        smp_threads = threads > 0 ? threads : 1;
> > -
> > -    }
> > -
> > -    if (max_cpus == 0) {
> > -        max_cpus = smp_cpus;
> > -    }
> > -
> > -    if (max_cpus > MAX_CPUMASK_BITS) {
> > -        error_report("unsupported number of maxcpus");
> > -        exit(1);
> > -    }
> > -    if (max_cpus < smp_cpus) {
> > -        error_report("maxcpus must be equal to or greater than smp");
> > -        exit(1);
> > +        smp_cores = cores;
> > +        smp_threads = threads;
> >      }
> >  
> > -    if (smp_cpus > 1 || smp_cores > 1 || smp_threads > 1) {
> > +    if (smp_cpus > 1) {
> >          Error *blocker = NULL;
> >          error_setg(&blocker, QERR_REPLAY_NOT_SUPPORTED, "smp");
> >          replay_add_blocker(blocker);
> 
>