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Re: [libvirt] [PATCH v4 2/2] libxl: implement NUMA capabilities reporting



Dario Faggioli wrote:
> Starting from Xen 4.2, libxl has all the bits and pieces in place
> for retrieving an adequate amount of information about the host
> NUMA topology. It is therefore possible, after a bit of shuffling,
> to arrange those information in the way libvirt wants to present
> them to the outside world.
>
> Therefore, with this patch, the <topology> section of the host
> capabilities is properly populated, when running on Xen, so that
> we can figure out whether or not we're running on a NUMA host,
> and what its characteristics are.
>
> [raistlin Zhaman ~]$ sudo virsh --connect xen:/// capabilities
> <capabilities>
>   <host>
>     <cpu>
>     ....
>     <topology>
>       <cells num='2'>
>         <cell id='0'>
>           <memory unit='KiB'>6291456</memory>
>           <cpus num='8'>
>             <cpu id='0' socket_id='1' core_id='0' siblings='0-1'/>
>             <cpu id='1' socket_id='1' core_id='0' siblings='0-1'/>
>             <cpu id='2' socket_id='1' core_id='1' siblings='2-3'/>
>             <cpu id='3' socket_id='1' core_id='1' siblings='2-3'/>
>             <cpu id='4' socket_id='1' core_id='9' siblings='4-5'/>
>             <cpu id='5' socket_id='1' core_id='9' siblings='4-5'/>
>             <cpu id='6' socket_id='1' core_id='10' siblings='6-7'/>
>             <cpu id='7' socket_id='1' core_id='10' siblings='6-7'/>
>           </cpus>
>         </cell>
>         <cell id='1'>
>           <memory unit='KiB'>6881280</memory>
>           <cpus num='8'>
>             <cpu id='8' socket_id='0' core_id='0' siblings='8-9'/>
>             <cpu id='9' socket_id='0' core_id='0' siblings='8-9'/>
>             <cpu id='10' socket_id='0' core_id='1' siblings='10-11'/>
>             <cpu id='11' socket_id='0' core_id='1' siblings='10-11'/>
>             <cpu id='12' socket_id='0' core_id='9' siblings='12-13'/>
>             <cpu id='13' socket_id='0' core_id='9' siblings='12-13'/>
>             <cpu id='14' socket_id='0' core_id='10' siblings='14-15'/>
>             <cpu id='15' socket_id='0' core_id='10' siblings='14-15'/>
>           </cpus>
>         </cell>
>       </cells>
>     </topology>
>   </host>
>   ....
>
> Signed-off-by: Dario Faggioli <dario faggioli citrix com>
> Cc: Daniel P. Berrange <berrange redhat com>
> ---
> Changes from v3:
>  * updated VIR_*ALLOC* call sites not to invoke virReportOOMError();
>  * failing at getting NUMA and CPU topology info from libxl are now
>    considered proper errors, as requested during review;
>  * s/out/cleanup/ as requested during review.
>
> Changes from v2:
>  * iterators turned from int to size_t;
>  * fixed wrong sibling maps if on same node but different socket;
>  * code motion and error handling, as requested during review.
>
> Changes from v1:
>  * fixed a typo in the commit message, as requested during review;
>  * fixed coding style (one function parameters per line and no spaces
>    between variable definitions), as requested during review;
>  * avoid zero-filling memory after VIR_ALLOC_N(), since it does that
>    already, as requested during review;
>  * improved out of memory error reporting, as requested during review;
>  * libxlMakeNumaCapabilities() created, accommodating all the NUMA
>    related additions, instead of having them within
>    libxlMakeCapabilitiesInternal(), as suggested during review.
> ---
>  src/libxl/libxl_conf.c |  140 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 139 insertions(+), 1 deletion(-)
>
> diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
> index 827dfdd..2c84191 100644
> --- a/src/libxl/libxl_conf.c
> +++ b/src/libxl/libxl_conf.c
> @@ -161,6 +161,107 @@ libxlBuildCapabilities(virArch hostarch,
>  }
>  
>  static virCapsPtr
> +libxlMakeNumaCapabilities(libxl_numainfo *numa_info,
> +                          int nr_nodes,
> +                          libxl_cputopology *cpu_topo,
> +                          int nr_cpus,
> +                          virCapsPtr caps)
>   

I know we discussed returning an int from this function to indicate
success/failure, and that I agreed with your reasoning [1] to keep the
virCapsPtr.  But now that driver init fails if gathering NUMA fails, I
think this really should return an int.

> +{
> +    virCapsHostNUMACellCPUPtr *cpus = NULL;
> +    int *nr_cpus_node = NULL;
> +    bool numa_failed = true;
> +    size_t i;
> +
> +    if (VIR_ALLOC_N(cpus, nr_nodes) < 0)
> +        goto cleanup;
> +
> +    if (VIR_ALLOC_N(nr_cpus_node, nr_nodes) < 0)
> +        goto cleanup;
> +
> +    /* For each node, prepare a list of CPUs belonging to that node */
> +    for (i = 0; i < nr_cpus; i++) {
> +        int node = cpu_topo[i].node;
> +
> +        if (cpu_topo[i].core == LIBXL_CPUTOPOLOGY_INVALID_ENTRY)
> +            continue;
> +
> +        nr_cpus_node[node]++;
> +
> +        if (nr_cpus_node[node] == 1) {
> +            if (VIR_ALLOC(cpus[node]) < 0)
> +                goto cleanup;
> +        } else {
> +            if (VIR_REALLOC_N(cpus[node], nr_cpus_node[node]) < 0)
> +                goto cleanup;
> +        }
> +
> +        /* Mapping between what libxl tells and what libvirt wants */
> +        cpus[node][nr_cpus_node[node]-1].id = i;
> +        cpus[node][nr_cpus_node[node]-1].socket_id = cpu_topo[i].socket;
> +        cpus[node][nr_cpus_node[node]-1].core_id = cpu_topo[i].core;
> +        /* Allocate the siblings maps. We will be filling them later */
> +        cpus[node][nr_cpus_node[node]-1].siblings = virBitmapNew(nr_cpus);
> +        if (!cpus[node][nr_cpus_node[node]-1].siblings) {
> +            virReportOOMError();
> +            goto cleanup;
> +        }
> +    }
> +
> +    /* Let's now populate the siblings bitmaps */
> +    for (i = 0; i < nr_cpus; i++) {
> +        int node = cpu_topo[i].node;
> +        size_t j;
> +
> +        if (cpu_topo[i].core == LIBXL_CPUTOPOLOGY_INVALID_ENTRY)
> +            continue;
> +
> +        for (j = 0; j < nr_cpus_node[node]; j++) {
> +            if (cpus[node][j].socket_id == cpu_topo[i].socket &&
> +                cpus[node][j].core_id == cpu_topo[i].core)
> +                ignore_value(virBitmapSetBit(cpus[node][j].siblings, i));
> +        }
> +    }
> +
> +    for (i = 0; i < nr_nodes; i++) {
> +        if (numa_info[i].size == LIBXL_NUMAINFO_INVALID_ENTRY)
> +            continue;
> +
> +        if (virCapabilitiesAddHostNUMACell(caps, i, nr_cpus_node[i],
> +                                           numa_info[i].size / 1024,
> +                                           cpus[i]) < 0) {
> +            virCapabilitiesClearHostNUMACellCPUTopology(cpus[i],
> +                                                        nr_cpus_node[i]);
> +            goto cleanup;
> +        }
> +
> +        /* This is safe, as the CPU list is now stored in the NUMA cell */
> +        cpus[i] = NULL;
> +    }
> +
> +    numa_failed = false;
> +
> + cleanup:
> +    if (numa_failed) {
> +        /* Something went wrong: deallocate everything and unref caps */
> +        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                       _("libxenlight failed to build the NUMA topology"));
> +
> +        for (i = 0; i < nr_nodes; i++) {
> +            VIR_FREE(cpus[i]);
> +        }
> +        virCapabilitiesFreeNUMAInfo(caps);
> +
> +        if (!virObjectUnref(caps))
> +            caps = NULL;
>   

I'm not fond of unref'ing caps and setting to NULL here, outside of the
function where caps was allocated.

I sent a patch to rework the capabilities code [2], which I think will
make it a bit easier to implement this function.  What do you think?

Regards,
Jim

[1] https://www.redhat.com/archives/libvir-list/2013-July/msg00458.html
[2] https://www.redhat.com/archives/libvir-list/2013-August/msg00543.html

> +    }
> +
> +    VIR_FREE(cpus);
> +    VIR_FREE(nr_cpus_node);
> +
> +    return caps;
> +}
> +
> +static virCapsPtr
>  libxlMakeCapabilitiesInternal(virArch hostarch,
>                                libxl_physinfo *phy_info,
>                                char *capabilities)
> @@ -876,7 +977,11 @@ libxlMakeCapabilities(libxl_ctx *ctx)
>  {
>      int err;
>      libxl_physinfo phy_info;
> +    libxl_numainfo *numa_info = NULL;
> +    libxl_cputopology *cpu_topo = NULL;
>      const libxl_version_info *ver_info;
> +    int nr_nodes = 0, nr_cpus = 0;
> +    virCapsPtr caps;
>  
>      err = regcomp(&xen_cap_rec, xen_cap_re, REG_EXTENDED);
>      if (err != 0) {
> @@ -900,9 +1005,42 @@ libxlMakeCapabilities(libxl_ctx *ctx)
>          return NULL;
>      }
>  
> -    return libxlMakeCapabilitiesInternal(virArchFromHost(),
> +    caps = libxlMakeCapabilitiesInternal(virArchFromHost(),
>                                           &phy_info,
>                                           ver_info->capabilities);
> +
> +    /* Check if caps is valid. If it is, it must remain so till the end! */
> +    if (caps == NULL)
> +        goto cleanup;
> +
> +    /* Let's try to fetch all the topology information */
> +    numa_info = libxl_get_numainfo(ctx, &nr_nodes);
> +    if (numa_info == NULL || nr_nodes == 0) {
> +        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                       _("libxl_get_numainfo failed"));
> +        goto cleanup;
> +    } else {
> +        cpu_topo = libxl_get_cpu_topology(ctx, &nr_cpus);
> +        if (cpu_topo == NULL || nr_cpus == 0) {
> +            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                           _("libxl_get_cpu_topology failed"));
> +            goto cleanup;
> +        }
> +        else {
> +            /* And add topology information to caps */
> +            caps = libxlMakeNumaCapabilities(numa_info,
> +                                             nr_nodes,
> +                                             cpu_topo,
> +                                             nr_cpus,
> +                                             caps);
> +        }
> +    }
> +
> +cleanup:
> +    libxl_cputopology_list_free(cpu_topo, nr_cpus);
> +    libxl_numainfo_list_free(numa_info, nr_nodes);
> +
> +    return caps;
>  }
>  
>  int
>
>
>
>   


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