Re: [Xen-devel] [PATCH v2] xl: introduce specific VCPU to PCPU mapping in config file

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2012-05-14 at 10:26 +0100, Dario Faggioli wrote:
> xm supports the following syntax (in the config file) for
> specific VCPU to PCPU mapping:
> 
> cpus = ["2", "3"] # VCPU0 runs on CPU2, VCPU1 runs on CPU3
> 
> Allow for the same in xl.
> 
> Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> 
> diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
> --- a/docs/man/xl.cfg.pod.5
> +++ b/docs/man/xl.cfg.pod.5
> @@ -108,9 +108,25 @@ created online and the remainder will be
>  =item B<cpus="CPU-LIST">
>  
>  List of which cpus the guest is allowed to use. Default behavior is
> -`all cpus`. A list of cpus may be specified as follows: `cpus="0-3,5,^1"`
> -(all vcpus will run on cpus 0,2,3,5), or `cpus=["2", "3"]` (all vcpus
> -will run on cpus 2 and 3).
> +`all cpus`. A C<CPU-LIST> may be specified as follows:
> +
> +=over 4
> +
> +=item "all"
> +
> +To allow all the vcpus of the guest tov run on all the cpus on the host.

typo:                                  to

> +
> +=item "0-3,5,^1"
> +
> +To allow all the vcpus of the guest to run on cpus 0,2,3,5.
> +
> +=item [2, 3]

Is this [2, 3] or ["2", "3"] as you used in the commit message? (would
it be confusing the make those distinct, represent the current xl
behaviour and xm behaviour respectively?)

I think you missed my review on the v1 code when preparing this posting
(we probably passed in mid-air)?

> +
> +To ask for specific vcpu mapping. That means (in this example), vcpu #0
> +of the guest will run on cpu #2 of the host and vcpu #1 of the guest will
> +run on cpu #3 of the host.
> +
> +=back
>  
>  =item B<cpu_weight=WEIGHT>
>  
> diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
> --- a/tools/libxl/xl_cmdimpl.c
> +++ b/tools/libxl/xl_cmdimpl.c
> @@ -71,6 +71,8 @@ static uint32_t domid;
>  static const char *common_domname;
>  static int fd_lock = -1;
>  
> +/* Stash for specific vcpu to pcpu mappping */
> +static int *vcpu_to_pcpu;
>  
>  static const char savefileheader_magic[32]=
>      "Xen saved domain, xl format\n \0 \r";
> @@ -630,6 +632,21 @@ static void parse_config_data(const char
>              exit(1);
>          }
>  
> +        /* Prepare the array for single vcpu to pcpu mappings */
> +        vcpu_to_pcpu = xmalloc(sizeof(int) * b_info->max_vcpus);
> +        memset(vcpu_to_pcpu, -1, sizeof(int) * b_info->max_vcpus);
> +
> +        /*
> +         * Idea here is to let libxl think all the domain's vcpus
> +         * have cpu affinity with all the pcpus on the list.
> +         * It is then us, here in xl, that matches each single vcpu
> +         * to its pcpu (and that's why we need to stash such info in
> +         * the vcpu_to_pcpu array now) after the domain has been created.
> +         * Doing it like this saves the burden of passing to libxl
> +         * some big array hosting the single mappings. Also, using
> +         * the cpumap derived from the list ensures memory is being
> +         * allocated on the proper nodes anyway.
> +         */
>          libxl_cpumap_set_none(&b_info->cpumap);
>          while ((buf = xlu_cfg_get_listitem(cpus, n_cpus)) != NULL) {
>              i = atoi(buf);
> @@ -638,6 +655,8 @@ static void parse_config_data(const char
>                  exit(1);
>              }
>              libxl_cpumap_set(&b_info->cpumap, i);
> +            if (n_cpus < b_info->max_vcpus)
> +                vcpu_to_pcpu[n_cpus] = i;
>              n_cpus++;
>          }
>      }
> @@ -1714,6 +1733,31 @@ start:
>      if ( ret )
>          goto error_out;
>  
> +    /* If single vcpu to pcpu mapping was requested, honour it */
> +    if (vcpu_to_pcpu) {
> +        libxl_cpumap vcpu_cpumap;
> +
> +        libxl_cpumap_alloc(ctx, &vcpu_cpumap);
> +        for (i = 0; i < d_config.b_info.max_vcpus; i++) {
> +
> +            if (vcpu_to_pcpu[i] != -1) {
> +                libxl_cpumap_set_none(&vcpu_cpumap);
> +                libxl_cpumap_set(&vcpu_cpumap, vcpu_to_pcpu[i]);
> +            } else {
> +                libxl_cpumap_set_any(&vcpu_cpumap);
> +            }
> +            if (libxl_set_vcpuaffinity(ctx, domid, i, &vcpu_cpumap)) {
> +                fprintf(stderr, "setting affinity failed on vcpu `%d'.\n", 
> i);
> +                libxl_cpumap_dispose(&vcpu_cpumap);
> +                free(vcpu_to_pcpu);
> +                ret = ERROR_FAIL;
> +                goto error_out;
> +            }
> +        }
> +        libxl_cpumap_dispose(&vcpu_cpumap);
> +        free(vcpu_to_pcpu);
> +    }
> +
>      ret = libxl_userdata_store(ctx, domid, "xl",
>                                      config_data, config_len);
>      if (ret) {



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