Re: [RFC PATCH v3 4/4] hw/arm/virt: Parse -smp cluster parameter in virt_smp_parse

[Andrew Jones]

On Tue, May 18, 2021 at 11:48:34AM +0800, wangyanan (Y) wrote:
> Hi Salil,
> 
> On 2021/5/17 23:17, Salil Mehta wrote:
> > > From: Qemu-devel
> > > [mailto:qemu-devel-bounces+salil.mehta=huawei.com@nongnu.org] On Behalf Of
> > > Yanan Wang
> > > Sent: Sunday, May 16, 2021 11:32 AM
> > > To: Peter Maydell <peter.maydell@linaro.org>; Paolo Bonzini
> > > <pbonzini@redhat.com>; Andrew Jones <drjones@redhat.com>; Michael S . 
> > > Tsirkin
> > > <mst@redhat.com>; Igor Mammedov <imammedo@redhat.com>; Shannon Zhao
> > > <shannon.zhaosl@gmail.com>; qemu-devel@nongnu.org; qemu-arm@nongnu.org
> > > Cc: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>; Philippe
> > > Mathieu-Daudé <philmd@redhat.com>; wangyanan (Y) <wangyanan55@huawei.com>;
> > > Zengtao (B) <prime.zeng@hisilicon.com>; Wanghaibin (D)
> > > <wanghaibin.wang@huawei.com>; yuzenghui <yuzenghui@huawei.com>; yangyicong
> > > <yangyicong@huawei.com>; zhukeqian <zhukeqian1@huawei.com>
> > > Subject: [RFC PATCH v3 4/4] hw/arm/virt: Parse -smp cluster parameter in
> > > virt_smp_parse
> > > 
> > > There is a separate function virt_smp_parse() in hw/virt/arm.c used
> > > to parse cpu topology for the ARM machines. So add parsing of -smp
> > > cluster parameter in it, then total number of logical cpus will be
> > > calculated like: max_cpus = sockets * clusters * cores * threads.
> > > 
> > > Note, we will assume multi-cluster in one socket is not supported
> > > and default the value of clusters to 1, if it's not explicitly
> > > specified in -smp cmdline.
> > > 
> > > Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> > > ---
> > >   hw/arm/virt.c | 32 ++++++++++++++++++--------------
> > >   1 file changed, 18 insertions(+), 14 deletions(-)
> > > 
> > > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > > index 7de822e491..678d5ef36c 100644
> > > --- a/hw/arm/virt.c
> > > +++ b/hw/arm/virt.c
> > > @@ -2642,8 +2642,8 @@ static int virt_kvm_type(MachineState *ms, const 
> > > char
> > > *type_str)
> > >    * with the -smp cmdlines when parsing them.
> > >    *
> > >    * We require that at least one of cpus or maxcpus must be provided.
> > > - * Threads will default to 1 if not provided. Sockets and cores must
> > > - * be either both provided or both not.
> > > + * Clusters and threads will default to 1 if they are not provided.
> > > + * Sockets and cores must be either both provided or both not.
> > >    *
> > >    * Note, if neither sockets nor cores are specified, we will calculate
> > >    * all the missing values just like smp_parse() does, but will disable
> > > @@ -2652,15 +2652,18 @@ static int virt_kvm_type(MachineState *ms, const 
> > > char
> > > *type_str)
> > >   static void virt_smp_parse(MachineState *ms, QemuOpts *opts)
> > >   {
> > >       VirtMachineClass *vmc = VIRT_MACHINE_GET_CLASS(ms);
> > > +    VirtMachineState *vms = VIRT_MACHINE(ms);
> > > 
> > >       if (opts) {
> > >           unsigned cpus = qemu_opt_get_number(opts, "cpus", 0);
> > >           unsigned maxcpus = qemu_opt_get_number(opts, "maxcpus", 0);
> > >           unsigned sockets = qemu_opt_get_number(opts, "sockets", 0);
> > > +        unsigned clusters = qemu_opt_get_number(opts, "clusters", 0);
> > >           unsigned cores = qemu_opt_get_number(opts, "cores", 0);
> > >           unsigned threads = qemu_opt_get_number(opts, "threads", 0);
> > > 
> > > -        /* Default threads to 1 if not provided */
> > > +        /* Default clusters and threads to 1 if not provided */
> > > +        clusters = clusters > 0 ? clusters : 1;
> > >           threads = threads > 0 ? threads : 1;
> > > 
> > >           if (cpus == 0 && maxcpus == 0) {
> > > @@ -2676,13 +2679,13 @@ static void virt_smp_parse(MachineState *ms, 
> > > QemuOpts
> > > *opts)
> > >               cores = 1;
> > >               if (cpus == 0) {
> > >                   sockets = 1;
> > > -                cpus = sockets * cores * threads;
> > > +                cpus = sockets * clusters * cores * threads;
> > >               } else {
> > >                   maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > > -                sockets = maxcpus / (cores * threads);
> > > +                sockets = maxcpus / (clusters * cores * threads);
> > >               }
> > >           } else if (sockets > 0 && cores > 0) {
> > > -            cpus = cpus > 0 ? cpus : sockets * cores * threads;
> > > +            cpus = cpus > 0 ? cpus : sockets * clusters * cores * 
> > > threads;
> > >               maxcpus = maxcpus > 0 ? maxcpus : cpus;
> > >           } else {
> > >               error_report("sockets and cores must be both provided "
> > > @@ -2695,25 +2698,26 @@ static void virt_smp_parse(MachineState *ms, 
> > > QemuOpts
> > > *opts)
> > >               exit(1);
> > >           }
> > > 
> > > -        if (sockets * cores * threads < cpus) {
> > > +        if (sockets * clusters * cores * threads < cpus) {
> > >               error_report("cpu topology: "
> > > -                         "sockets (%u) * cores (%u) * threads (%u) < "
> > > -                         "smp_cpus (%u)",
> > > -                         sockets, cores, threads, cpus);
> > > +                         "sockets (%u) * clusters (%u) * cores (%u) * "
> > > +                         "threads (%u) < smp_cpus (%u)",
> > > +                         sockets, clusters, cores, threads, cpus);
> > >               exit(1);
> > >           }
> > > 
> > > -        if (sockets * cores * threads != maxcpus) {
> > > +        if (sockets * clusters * cores * threads != maxcpus) {
> > >               error_report("cpu topology: "
> > > -                         "sockets (%u) * cores (%u) * threads (%u) "
> > > -                         "!= maxcpus (%u)",
> > > -                         sockets, cores, threads, maxcpus);
> > > +                         "sockets (%u) * clusters (%u) * cores (%u) * "
> > > +                         "threads (%u) != maxcpus (%u)",
> > > +                         sockets, clusters, cores, threads, maxcpus);
> > >               exit(1);
> > >           }
> > > 
> > >           ms->smp.cpus = cpus;
> > >           ms->smp.max_cpus = maxcpus;
> > >           ms->smp.sockets = sockets;
> > > +        vms->smp_clusters = clusters;
> > 
> > This variable naming *smp_clusters* looks out-of-sorts. I thought a similar
> > variable *smp_cpus* was destined to be removed for the reason given in below
> > link - a patch by Andrew Jones?
> > 
> > Link: https://lists.gnu.org/archive/html/qemu-arm/2020-12/msg00418.html
> > 
> > Am I missing anything here?
> The smp_clusters is added in VirtMachineState and nowhere else because
> it's currently only used for ARM. But I think maybe I should also move it to
> CpuTopology structure like [1] is doing to move dies to CpuTopology.

Yes, please do that.

Thanks,
drew

> 
> Move clusters to CpuTopology won't affect other architectures that don't
> support it yet, and will also make it easy if they want to in the future.
> 
> [1] From Paolo:
> 20210513162901.1310239-10-pbonzini@redhat.com/">https://patchwork.kernel.org/project/qemu-devel/patch/20210513162901.1310239-10-pbonzini@redhat.com/
> 
> Thanks,
> Yanan
> > Salil.
> > 
> > >           ms->smp.cores = cores;
> > >           ms->smp.threads = threads;
> > >       }
> > .
>