Re: [PATCH 4/4] NUMA: realize NUMA memory pinning

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Aug 11, 2010 at 03:52:18PM +0200, Andre Przywara wrote:
> According to the user-provided assignment bind the respective part
> of the guest's memory to the given host node. This uses Linux'
> mbind syscall (which is wrapped only in libnuma) to realize the
> pinning right after the allocation.
> Failures are not fatal, but produce a warning.
> 
> Signed-off-by: Andre Przywara <andre.przywara@amd.com>
> ---
>  hw/pc.c |   58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 58 insertions(+), 0 deletions(-)
> 
> diff --git a/hw/pc.c b/hw/pc.c
> index 1b24409..dbfc082 100644
> --- a/hw/pc.c
> +++ b/hw/pc.c
> @@ -42,6 +42,15 @@
>  #include "device-assignment.h"
>  #include "kvm.h"
>  
> +#ifdef CONFIG_NUMA
> +#include <numa.h>
> +#include <numaif.h>
> +#ifndef MPOL_F_RELATIVE_NODES
> +  #define MPOL_F_RELATIVE_NODES (1 << 14)
> +  #define MPOL_F_STATIC_NODES (1 << 15)
> +#endif
> +#endif
> +
>  /* output Bochs bios info messages */
>  //#define DEBUG_BIOS
>  
> @@ -882,6 +891,53 @@ void pc_cpus_init(const char *cpu_model)
>      }
>  }
>  
> +static void bind_numa(ram_addr_t ram_addr)
> +{
> +#ifdef CONFIG_NUMA
> +    int i;
> +    char* ram_ptr;
> +    ram_addr_t len, ram_offset;
> +    int bind_mode;
> +
> +    ram_ptr = qemu_get_ram_ptr(ram_addr);
> +
> +    ram_offset = 0;
> +    for (i = 0; i < nb_numa_nodes; i++) {
> +        len = numa_info[i].guest_mem;
> +        if (numa_info[i].flags != 0) {
> +            switch (numa_info[i].flags & NODE_HOST_POLICY_MASK) {
> +            case NODE_HOST_BIND:
> +                bind_mode = MPOL_BIND;
> +                break;
> +            case NODE_HOST_INTERLEAVE:
> +                bind_mode = MPOL_INTERLEAVE;
> +                break;
> +            case NODE_HOST_PREFERRED:
> +                bind_mode = MPOL_PREFERRED;
> +                break;
> +            default:
> +                bind_mode = MPOL_DEFAULT;
> +                break;
> +            }
> +            bind_mode |= (numa_info[i].flags & NODE_HOST_RELATIVE) ?
> +                MPOL_F_RELATIVE_NODES : MPOL_F_STATIC_NODES;
> +
> +            /* This is a workaround for a long standing bug in Linux'
> +             * mbind implementation, which cuts off the last specified
> +             * node. To stay compatible should this bug be fixed, we
> +             * specify one more node and zero this one out.
> +             */
> +            clear_bit(numa_num_configured_nodes() + 1, numa_info[i].host_mem);
> +            if (mbind(ram_ptr + ram_offset, len, bind_mode,
> +                numa_info[i].host_mem, numa_num_configured_nodes() + 1, 0))
> +                    perror("mbind");
> +        }
> +        ram_offset += len;
> +    }
> +#endif

Why is it not possible (or perhaps not desired) to change the binding
after the guest is started?

Sounds unflexible.