Re: [Qemu-devel] [Qemu-ppc] [QEMU-PPC] [PATCH] powerpc/spapr: Add host threads parameter to ibm, get_system_parameter

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

On Mon, 2019-06-24 at 10:37 +0200, Greg Kurz wrote:
> On Mon, 24 Jun 2019 11:39:21 +1000
> Suraj Jitindar Singh <sjitindarsingh@gmail.com> wrote:
> 
> > The ibm,get_system_parameter rtas call is used by the guest to
> > retrieve
> > data relating to certain parameters of the system. The SPLPAR
> > characteristics option (token 20) is used to determin
> > characteristics of
> > the environment in which the lpar will run.
> > 
> > It may be useful for a guest to know the number of physical host
> > threads
> > present on the underlying system where it is being run. Add the
> > characteristic "HostThrs" to the SPLPAR Characteristics
> > ibm,get_system_parameter rtas call to expose this information to a
> > guest and provide an implementation which determines this
> > information
> > based on the number of interrupt servers present in the device
> > tree.
> > 
> 
> Shouldn't this also take split core into account, ie. divide the
> result by "/sys/devices/system/cpu/subcores_per_core" like the 
> ppc64_cpu command from powerpc-utils does ?

That makes sense, I'll modify the code to account for that.

Thanks,
Suraj

> 
> > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> > ---
> >  hw/ppc/spapr_rtas.c | 44
> > ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> > 
> > diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> > index 5bc1a93271..a33d87794c 100644
> > --- a/hw/ppc/spapr_rtas.c
> > +++ b/hw/ppc/spapr_rtas.c
> > @@ -229,6 +229,40 @@ static inline int sysparm_st(target_ulong
> > addr, target_ulong len,
> >      return RTAS_OUT_SUCCESS;
> >  }
> >  
> > +static int rtas_get_num_host_threads(void)
> > +{
> > +    const char *entry, *name = "/proc/device-tree/cpus/";
> > +    int num_threads = -1;
> > +    GDir *dir;
> > +
> > +    if (!kvm_enabled())
> > +        return 1;
> > +
> > +    dir = g_dir_open(name, 0, NULL);
> > +    if (!dir)
> > +        return -1;
> > +
> > +    while ((entry = g_dir_read_name(dir))) {
> > +        if (!strncmp(entry, "PowerPC,POWER",
> > strlen("PowerPC,POWER"))) {
> > +            unsigned long len;
> > +            char *path, *buf;
> > +
> > +            path = g_strconcat(name, entry, "/ibm,ppc-interrupt-
> > server#s",
> > +                               NULL);
> > +            if (g_file_get_contents(path, &buf, &len, NULL)) {
> > +                num_threads = len / sizeof(int);
> > +                g_free(buf);
> > +            }
> > +
> > +            g_free(path);
> > +            break;
> > +        }
> > +    }
> > +
> > +    g_dir_close(dir);
> > +    return num_threads;
> > +}
> > +
> >  static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
> >                                            SpaprMachineState
> > *spapr,
> >                                            uint32_t token, uint32_t
> > nargs,
> > @@ -250,6 +284,16 @@ static void
> > rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
> >                                            current_machine-
> > >ram_size / MiB,
> >                                            smp_cpus,
> >                                            max_cpus);
> > +        int num_host_threads = rtas_get_num_host_threads();
> > +
> > +        if (num_host_threads > 0) {
> > +            char *hostthr_val, *old = param_val;
> > +
> > +            hostthr_val = g_strdup_printf(",HostThrs=%d",
> > num_host_threads);
> > +            param_val = g_strconcat(param_val, hostthr_val, NULL);
> > +            g_free(hostthr_val);
> > +            g_free(old);
> > +        }
> >          ret = sysparm_st(buffer, length, param_val,
> > strlen(param_val) + 1);
> >          g_free(param_val);
> >          break;
> 
>