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Re: [libvirt] [PATCH] nodeinfo: Get the correct CPU number on AMD Magny Cours platform



On 05/14/2012 04:25 AM, Osier Yang wrote:
"Instead of developing one CPU with 12 cores, the Magny Cours is
actually two 6 core “Bulldozer” CPUs combined in to one package"

I.e, each package has two NUMA nodes, and the two numa nodes share
the same core ID set (0-6), which means parsing the cores number
from sysfs doesn't work in this case.

And the wrong CPU number could cause three problems for libvirt:

1) performance lost

   A domain without "cpuset" or "placement='auto'" (to drive numad)
specified will be only pinned to part of the CPUs.

2) domain can be started

   If a domain uses numad, and the advisory nodeset returned from
numad contains node which exceeds the range of wrong total CPU
number. The domain will fail to start, as the bitmask passed to
sched_setaffinity could be fully filled with zero.

3) wrong CPU number affects lots of stuffs.

   E.g. for command "virsh vcpuinfo", "virsh vcpupin", it will always
output with the truncated CPU list.

For more details:

https://www.redhat.com/archives/libvir-list/2012-May/msg00607.html

This patch is to fix the problem by parsing /proc/cpuinfo to get
the value of field "cpu cores", and use it as nodeinfo->cores if
it's greater than the cores number from sysfs.

@@ -265,6 +266,22 @@ int linuxNodeInfoCPUPopulate(FILE *cpuinfo,
                  &&  (*p == '\0' || *p == '.' || c_isspace(*p)))
                  nodeinfo->mhz = ui;
          }
+
+        if (STRPREFIX(buf, "cpu cores")) {
+            char *p;
+            unsigned int ui;
+            buf += 9;

Nit: empty line after var. declaration.

+            while (*buf&&  c_isspace(*buf))
+                buf++;
+            if (*buf != ':' || !buf[1]) {
+                nodeReportError(VIR_ERR_INTERNAL_ERROR,
+                                "%s", _("parsing cpuinfo cpu MHz"));
+                return -1;
+            }

This should probably say _("parsing number of CPU cores")

   Stefan


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