Re: [RFC PATCH 4/6] machine: Uniformly use maxcpus to calculate the missing values

[wangyanan (Y)]

Hi Drew,

On 2021/7/12 23:25, Andrew Jones wrote:
> On Fri, Jul 02, 2021 at 06:07:37PM +0800, Yanan Wang wrote:
> > We are currently using maxcpus to calculate value of sockets but using
> > cpus to calculate value of cores/threads. This makes cmdlines like
> > "-smp 8,maxcpus=12,cores=4" work while "-smp 8,maxcpus=12,sockets=3"
> > break the invalid cpu topology check.
> >
> > This patch allows us to uniformly use maxcpus to calculate the missing
> > values. Also the if branch of "cpus == 0 || sockets == 0" was splited
> > into branches of "cpus == 0" and "sockets == 0" so that we can clearly
> > figure out that we are parsing -smp cmdlines with a preference of cpus
> > over sockets over cores over threads.
> >
> > Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> > ---
> >   hw/core/machine.c | 36 +++++++++++++++++++-----------------
> >   hw/i386/pc.c      | 37 +++++++++++++++++++------------------
> >   2 files changed, 38 insertions(+), 35 deletions(-)
> >
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index 1e194677cd..58882835be 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -752,34 +752,36 @@ static void smp_parse(MachineState *ms, SMPConfiguration 
> > *config, Error **errp)
> >       }
> >   
> >       /* compute missing values, prefer sockets over cores over threads */
> > -    if (cpus == 0 || sockets == 0) {
> > +    maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > +
> > +    if (cpus == 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 {
> > -            maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > -            sockets = maxcpus / (cores * threads);
> > -            sockets = sockets > 0 ? sockets : 1;
> > -        }
> > +        cpus = sockets * cores * threads;
> > +        maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > +    } else if (sockets == 0) {
> > +        cores = cores > 0 ? cores : 1;
> > +        threads = threads > 0 ? threads : 1;
> > +        sockets = maxcpus / (cores * threads);
> > +        sockets = sockets > 0 ? sockets : 1;
> As stated in the other patch, this rounding up of a fractional sockets
> shouldn't be here. maxcpus or (cpus==maxcpus) should always be selected by
> the user to be a product of whole number sockets, cores, threads.
I also default sockets to 1 if computed as zero because we are doing
this for cores/threads and I did't see the difference between them.

Anyway, now that we are using maxcpus for all calculations, so we can
either get rid of all the rounding-ups for sockets/cores/threads or just
keep them all.

With the rouding-up, we get:
-smp cpus=12,cores=16,maxcpus=12 --> -smp 
cpus=12,sockets=0,cores=16,threads=1,maxcpus=12 --> error_report

without the rounding-up we get:
-smp cpus=12,cores=16,maxcpus=12 --> -smp 
cpus=12,sockets=1,cores=16,threads=1,maxcpus=12 --> error_report

We will both get an error report as expected, but I can get rid of the 
rounding if it's preferred.
> >       } else if (cores == 0) {
> >           threads = threads > 0 ? threads : 1;
> > -        cores = cpus / (sockets * threads);
> > +        cores = maxcpus / (sockets * threads);
> >           cores = cores > 0 ? cores : 1;
> Now that we're using maxcpus for the calculation, then no rounding for
> cores either...
>
> >       } else if (threads == 0) {
> > -        threads = cpus / (cores * sockets);
> > +        threads = maxcpus / (sockets * cores);
> >           threads = threads > 0 ? threads : 1;
> ...or threads.
>
> > -    } else if (sockets * cores * threads < cpus) {
> > +    }
> > +
> > +    if (sockets * cores * threads < cpus) {
> >           error_setg(errp, "cpu topology: "
> > -                   "sockets (%u) * cores (%u) * threads (%u) < "
> > -                   "smp_cpus (%u)",
> > +                   "sockets (%u) * cores (%u) * threads (%u) "
> > +                   "< smp_cpus (%u)",
> Why make this change?
No need actually, will change it back. :)
> >                      sockets, cores, threads, cpus);
> >           return;
> >       }
> >   
> > -    maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > -
> >       if (maxcpus < cpus) {
> >           error_setg(errp, "maxcpus must be equal to or greater than smp");
> >           return;
> > @@ -795,9 +797,9 @@ static void smp_parse(MachineState *ms, SMPConfiguration 
> > *config, Error **errp)
> >       }
> >   
> >       ms->smp.cpus = cpus;
> > +    ms->smp.sockets = sockets;
> >       ms->smp.cores = cores;
> >       ms->smp.threads = threads;
> > -    ms->smp.sockets = sockets;
> >       ms->smp.max_cpus = maxcpus;
> >   }
> >   
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 93d1f12a49..1812f33ab1 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -721,35 +721,36 @@ static void pc_smp_parse(MachineState *ms, 
> > SMPConfiguration *config, Error **err
> >   
> >       /* compute missing values, prefer sockets over cores over threads */
> >       dies = dies > 0 ? dies : 1;
> > +    maxcpus = maxcpus > 0 ? maxcpus : cpus;
> >   
> > -    if (cpus == 0 || sockets == 0) {
> > +    if (cpus == 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 * dies * sockets;
> > -        } else {
> > -            maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > -            sockets = maxcpus / (dies * cores * threads);
> > -            sockets = sockets > 0 ? sockets : 1;
> > -        }
> > +        cpus = sockets * dies * cores * threads;
> > +        maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > +    } else if (sockets == 0) {
> > +        cores = cores > 0 ? cores : 1;
> > +        threads = threads > 0 ? threads : 1;
> > +        sockets = maxcpus / (dies * cores * threads);
> > +        sockets = sockets > 0 ? sockets : 1;
> >       } else if (cores == 0) {
> >           threads = threads > 0 ? threads : 1;
> > -        cores = cpus / (sockets * dies * threads);
> > +        cores = maxcpus / (sockets * dies * threads);
> >           cores = cores > 0 ? cores : 1;
> >       } else if (threads == 0) {
> > -        threads = cpus / (cores * dies * sockets);
> > +        threads = maxcpus / (sockets * dies * cores);
> >           threads = threads > 0 ? threads : 1;
> > -    } else if (sockets * dies * cores * threads < cpus) {
> > +    }
> > +
> > +    if (sockets * dies * cores * threads < cpus) {
> >           error_setg(errp, "cpu topology: "
> > -                   "sockets (%u) * dies (%u) * cores (%u) * threads (%u) < "
> > -                   "smp_cpus (%u)",
> > +                   "sockets (%u) * dies (%u) * cores (%u) * threads (%u) "
> > +                   "< smp_cpus (%u)",
> >                      sockets, dies, cores, threads, cpus);
> >           return;
> >       }
> >   
> Same comments as for the general function.
>
> Thanks,
> drew
>
> > -    maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > -
> >       if (maxcpus < cpus) {
> >           error_setg(errp, "maxcpus must be equal to or greater than smp");
> >           return;
> > @@ -765,10 +766,10 @@ static void pc_smp_parse(MachineState *ms, 
> > SMPConfiguration *config, Error **err
> >       }
> >   
> >       ms->smp.cpus = cpus;
> > -    ms->smp.cores = cores;
> > -    ms->smp.threads = threads;
> >       ms->smp.sockets = sockets;
> >       ms->smp.dies = dies;
> > +    ms->smp.cores = cores;
> > +    ms->smp.threads = threads;
> >       ms->smp.max_cpus = maxcpus;
> >   }
> >   
> > --
> > 2.19.1
Thanks,
Yanan
.
> .