Re: [Qemu-devel] [RFCv2 1/2] pseries: Fix incorrect calculation of threads per socket for chip-id

[David Gibson]

On Fri, Sep 04, 2015 at 02:51:39PM +1000, David Gibson wrote:
> The device tree presented to pseries machine type guests includes an
> ibm,chip-id property which gives essentially the socket number of each
> vcpu core (individual vcpu threads don't get a node in the device
> tree).
> 
> To calculate this, it uses a vcpus_per_socket variable computed as
> (smp_cpus / #sockets).  This is correct for the usual case where
> smp_cpus == smp_threads * smp_cores * #sockets.
> 
> However, you can start QEMU with the number of cores and threads
> mismatching the total number of vcpus (whether that _should_ be
> permitted is a topic for another day).  It's a bit hard to say what
> the "real" number of vcpus per socket here is, but for most purposes
> (smp_threads * smp_cores) will more meaningfully match how QEMU
> behaves with respect to socket boundaries.
> 
> Signed-off-by: David Gibson <address@hidden>

Gah, sorry, there's a compile error in this.  I got sidetracked
between writing and posting and forgot I hadn't fixed it yet.

> ---
>  hw/ppc/spapr.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 783763f..dbc295b 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -595,8 +595,7 @@ static void spapr_populate_cpu_dt(CPUState *cs, void 
> *fdt, int offset,
>      uint32_t page_sizes_prop[64];
>      size_t page_sizes_prop_size;
>      QemuOpts *opts = qemu_opts_find(qemu_find_opts("smp-opts"), NULL);
> -    unsigned sockets = opts ? qemu_opt_get_number(opts, "sockets", 0) : 0;
> -    uint32_t cpus_per_socket = sockets ? (smp_cpus / sockets) : 1;
> +    uint32_t vcpus_per_socket = smp_threads * smp_cores;
>      uint32_t pft_size_prop[] = {0, cpu_to_be32(spapr->htab_shift)};
>  
>      _FDT((fdt_setprop_cell(fdt, offset, "reg", index)));
> @@ -665,7 +664,7 @@ static void spapr_populate_cpu_dt(CPUState *cs, void 
> *fdt, int offset,
>      }
>  
>      _FDT((fdt_setprop_cell(fdt, offset, "ibm,chip-id",
> -                           cs->cpu_index / cpus_per_socket)));
> +                           cs->cpu_index / vcpus_per_socket)));
>  
>      _FDT((fdt_setprop(fdt, offset, "ibm,pft-size",
>                        pft_size_prop, sizeof(pft_size_prop))));

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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