[libvirt] [Qemu-devel] [PATCH v5 2/2] vl:c: make sure that sockets are calculated correctly in '-smp X' case

[Eduardo Habkost]

On Tue, Sep 04, 2018 at 05:18:48PM +0200, Andrew Jones wrote:
> On Tue, Sep 04, 2018 at 03:22:36PM +0200, Igor Mammedov wrote:
> > commit
> >   (5cdc9b76e3 vl.c: Remove dead assignment)
> > removed sockets calculation when 'sockets' weren't provided on CLI
> > since there wasn't any users for it back then. Exiting checks
> > are neither reachable
> >    } else if (sockets * cores * threads < cpus) {
> > or nor triggable
> >    if (sockets * cores * threads > max_cpus)
> > so we weren't noticing wrong topology since then, since users
> > recalculate sockets adhoc on their own.
> > 
> > However with deprecation check it becomes noticable, for example
> >   -smp 2
> > will start printing warning:
> >   "warning: Invalid CPU topology deprecated: sockets (1) * cores (1) * threads (1) != maxcpus (2)"
> > calculating sockets if they weren't specified.
> > 
> > Fix it by returning back sockets calculation if it's omited on CLI.
> > 
> > Signed-off-by: Igor Mammedov <imammedo at redhat.com>
> > ---
> >  vl.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/vl.c b/vl.c
> > index 7fd700e..333d638 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -1210,11 +1210,14 @@ static void smp_parse(QemuOpts *opts)
> >  
> >          /* compute missing values, prefer sockets over cores over threads */
> >          if (cpus == 0 || sockets == 0) {
> > -            sockets = sockets > 0 ? sockets : 1;
> >              cores = cores > 0 ? cores : 1;
> >              threads = threads > 0 ? threads : 1;
> >              if (cpus == 0) {
> > +                sockets = sockets > 0 ? sockets : 1;
> >                  cpus = cores * threads * sockets;
> > +            } else {
> > +                max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
> > +                sockets = !sockets ? max_cpus / (cores * threads) : sockets;

Why the !sockets check here?  If we have reached this statement
we know that (cpus == 0 || sockets == 0) is true and
(cpus == 0) is false, so sockets is guaranteed to be 0.

Sorry for not spotting this earlier.

> >              }
> >          } else if (cores == 0) {
> >              threads = threads > 0 ? threads : 1;
> > -- 
> > 2.7.4
> > 
> >
>  
> Reviewed-by: Andrew Jones <drjones at redhat.com>

-- 
Eduardo