Re: [RFC PATCH 3/6] pc/machine: Perform zero-check for the value of -smp dies

[wangyanan (Y)]

On 2021/7/12 23:27, Andrew Jones wrote:
> On Mon, Jul 12, 2021 at 05:05:43PM +0200, Andrew Jones wrote:
> > On Mon, Jul 12, 2021 at 05:04:04PM +0200, Andrew Jones wrote:
> > > On Fri, Jul 02, 2021 at 06:07:36PM +0800, Yanan Wang wrote:
> > > > It's possible that dies parameter is explicitly specified as "dies=0"
> > > > in the cmdline, if so we will wrongly calculate the other ommited
> > > > parameters such as "sockets = maxcpus / (dies * cores * threads);"
> > > > with a zeroed dies value.
> > > >
> > > > So perform zero-check (default the value to 1 if zeroed) for -smp dies
> > > > before using it to calculate other parameters.
> > > OK, dies=0 may make some sense for a user that doesn't want to describe
> > > dies.
> > >
> > > Reviewed-by: Andrew Jones <drjones@redhat.com>
> > But... this is the pc smp parse function, not the general one, so maybe my
> > comment from patch 1 should apply here as well, which is, that dies=0
> > should be an error rather than silently changed to dies=1.
> Also, after reading Daniel's comment on a later patch, I think anything=0
> should just be an error, even for the general parser.
Ok, after reading comments in patch #1, I also agree with this solution.
We can reject the "anything = 0" configuration in advance in function
machine_smp_parse(). I will do it in v2.

BTW, I have converted smp_parse() into a generic helper allowing future
extension for new arch-specific parameters, as you have suggested.
So that we don't need to maintain duplicated parsing code any more.

Thanks,
Yanan
.
> > > > Fixes: 1b45842203540 (vl.c: Add -smp, dies=* command line support and update 
> > > > doc)
> > > > Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> > > > ---
> > > >   hw/i386/pc.c | 4 +++-
> > > >   1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > > index a44511c937..93d1f12a49 100644
> > > > --- a/hw/i386/pc.c
> > > > +++ b/hw/i386/pc.c
> > > > @@ -714,12 +714,14 @@ static void pc_smp_parse(MachineState *ms, 
> > > > SMPConfiguration *config, Error **err
> > > >   {
> > > >       unsigned cpus    = config->has_cpus ? config->cpus : 0;
> > > >       unsigned sockets = config->has_sockets ? config->sockets : 0;
> > > > -    unsigned dies    = config->has_dies ? config->dies : 1;
> > > > +    unsigned dies    = config->has_dies ? config->dies : 0;
> > > >       unsigned cores   = config->has_cores ? config->cores : 0;
> > > >       unsigned threads = config->has_threads ? config->threads : 0;
> > > >       unsigned maxcpus = config->has_maxcpus ? config->maxcpus : 0;
> > > >   
> > > >       /* compute missing values, prefer sockets over cores over threads */
> > > > +    dies = dies > 0 ? dies : 1;
> > > > +
> > > >       if (cpus == 0 || sockets == 0) {
> > > >           cores = cores > 0 ? cores : 1;
> > > >           threads = threads > 0 ? threads : 1;
> > > > --
> > > > 2.19.1
> .