Re: [Qemu-devel] [PATCH 2/3] spapr: do not use CPU_FOREACH_REVERSE

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Aug 13, 2018 at 12:38:58PM -0400, Emilio G. Cota wrote:
> This paves the way for implementing the CPU list with an RCU QLIST,
> which cannot be traversed in reverse order.
> 
> Note that this is the only caller of CPU_FOREACH_REVERSE.
> 
> Signed-off-by: Emilio G. Cota <cota@braap.org>

Acked-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  hw/ppc/spapr.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 421b2dd09b..2ef5be2790 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -622,9 +622,12 @@ static void spapr_populate_cpu_dt(CPUState *cs, void *fdt, int offset,
>  
>  static void spapr_populate_cpus_dt_node(void *fdt, sPAPRMachineState *spapr)
>  {
> +    CPUState **rev;
>      CPUState *cs;
> +    int n_cpus;
>      int cpus_offset;
>      char *nodename;
> +    int i;
>  
>      cpus_offset = fdt_add_subnode(fdt, 0, "cpus");
>      _FDT(cpus_offset);
> @@ -635,8 +638,19 @@ static void spapr_populate_cpus_dt_node(void *fdt, sPAPRMachineState *spapr)
>       * We walk the CPUs in reverse order to ensure that CPU DT nodes
>       * created by fdt_add_subnode() end up in the right order in FDT
>       * for the guest kernel the enumerate the CPUs correctly.
> +     *
> +     * The CPU list cannot be traversed in reverse order, so we need
> +     * to do extra work.
>       */
> -    CPU_FOREACH_REVERSE(cs) {
> +    n_cpus = 0;
> +    rev = NULL;
> +    CPU_FOREACH(cs) {
> +        rev = g_renew(CPUState *, rev, n_cpus + 1);
> +        rev[n_cpus++] = cs;
> +    }
> +
> +    for (i = n_cpus - 1; i >= 0; i--) {
> +        CPUState *cs = rev[i];
>          PowerPCCPU *cpu = POWERPC_CPU(cs);
>          int index = spapr_get_vcpu_id(cpu);
>          DeviceClass *dc = DEVICE_GET_CLASS(cs);

-- 
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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