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Re: [libvirt] [PATCH v3 1/3] libxl: implement NUMA capabilities reporting



On Sat, Jul 13, 2013 at 02:27:03AM +0200, 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>
> ---
> 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 |  148 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 147 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
> index 4a0fba9..c097d1e 100644
> --- a/src/libxl/libxl_conf.c
> +++ b/src/libxl/libxl_conf.c
> @@ -161,6 +161,117 @@ libxlBuildCapabilities(virArch hostarch,
>  }
>  
>  static virCapsPtr
> +libxlMakeNumaCapabilities(libxl_numainfo *numa_info,
> +                          int nr_nodes,
> +                          libxl_cputopology *cpu_topo,
> +                          int nr_cpus,
> +                          virCapsPtr caps)
> +{
> +    virCapsHostNUMACellCPUPtr *cpus = NULL;
> +    int *nr_cpus_node = NULL;
> +    bool numa_failed = false;
> +    size_t i;
> +
> +    if (VIR_ALLOC_N(cpus, nr_nodes)) {
> +        virReportOOMError();
> +        return caps;
> +    }
> +
> +    if (VIR_ALLOC_N(nr_cpus_node, nr_nodes)) {
> +        VIR_FREE(cpus);
> +        virReportOOMError();
> +        return caps;
> +    }

Afraid some more changes have landed in GIT that affect you.

All the VIR_*ALLOC* functions, except those suffixed _QUIET
will now call virReportOOMError() for you. So you can remove
virReportOOMError here and all other places related to these
alloc fnuctions.

Also, you should be checking  'VIR_ALLOC_N() < 0', not just
for a non-zero value.

> +
> +    /* 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) {
> +                virReportOOMError();
> +                numa_failed = true;
> +                goto cleanup;
> +            }
> +        }
> +        else {
> +            if (VIR_REALLOC_N(cpus[node], nr_cpus_node[node]) < 0) {
> +                virReportOOMError();
> +                numa_failed = true;
> +                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();
> +            numa_failed = true;
> +            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]);
> +            numa_failed = true;
> +            goto cleanup;
> +        }
> +
> +        /* This is safe, as the CPU list is now stored in the NUMA cell */
> +        cpus[i] = NULL;
> +    }
> +
> + cleanup:
> +
> +    if (numa_failed) {
> +        /* Looks like something went wrong. Well, that's bad, but probably
> +         * not enough to break the whole driver, so we log and carry on */
> +        for (i = 0; i < nr_nodes; i++) {
> +            VIR_FREE(cpus[i]);
> +        }
> +        VIR_WARN("Failed to retrieve and build host NUMA topology properly,\n"
> +                 "disabling NUMA capabilities");
> +        virCapabilitiesFreeNUMAInfo(caps);

This is wrong. All the cases of error leading to this point are out of
memory errors. It is madness to prevent everything is ok & carry on here.
This should be treated as a proper error.


> @@ -788,9 +903,40 @@ 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 out;
> +
> +    /* Let's try to fetch NUMA info now (not critical in case we fail) */
> +    numa_info = libxl_get_numainfo(ctx, &nr_nodes);
> +    if (numa_info == NULL)
> +        VIR_WARN("libxl_get_numainfo failed to retrieve NUMA data");

Under what scenario can libxl_get_numainfo() return NULL ? Unless this
is an valid expected scenario, we should treat this is an error.

> +    else {
> +        /* If the above failed, we'd have no NUMa caps anyway! */
> +        cpu_topo = libxl_get_cpu_topology(ctx, &nr_cpus);
> +        if (cpu_topo == NULL) {
> +            VIR_WARN("libxl_get_cpu_topology failed to retrieve topology");
> +            libxl_numainfo_list_free(numa_info, nr_nodes);
> +        }

Likewise here.

> +        else {
> +            /* And add topology information to caps */
> +            caps = libxlMakeNumaCapabilities(numa_info,
> +                                             nr_nodes,
> +                                             cpu_topo,
> +                                             nr_cpus,
> +                                             caps);
> +        }
> +    }
> +
> +    libxl_cputopology_list_free(cpu_topo, nr_cpus);
> +    libxl_numainfo_list_free(numa_info, nr_nodes);
> +
> +out:

s/out/cleanup/ is our preferred label naming

> +    return caps;
>  }

Regards,
Daniel
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