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

[Andrew Jones]

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.

>      } 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?

>                     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
>