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Re: [libvirt] [PATCH 3/3] qemu: Generate -numa command line option

On 11/06/2011 06:59 AM, Bharata B Rao wrote:
qemu: Generate -numa option

From: Bharata B Rao<bharata linux vnet ibm com>

Add routines to generate -numa QEMU command line option based on
<numa>  ...</numa>  XML specifications.

Signed-off-by: Bharata B Rao<bharata linux vnet ibm com>

+static int
+qemuBuildNumaCPUArgStr(char *cpumask, virBufferPtr buf)
+    int i, first, last;
+    int cpuSet = 0;

What happens if cpumask is all 0?

+    for (i = 0; i<  VIR_DOMAIN_CPUMASK_LEN; i++) {
+        if (cpumask[i]) {

This if branch is skipped,

+            if (cpuSet)
+                last = i;
+            else {
+                first = last = i;
+                cpuSet = 1;
+            }
+        } else {
+            if (!cpuSet)
+                continue;

so this branch always continues,

+            if (first == last)
+                virBufferAsprintf(buf, "%d,", first);
+            else
+                virBufferAsprintf(buf, "%d-%d,", first, last);
+            cpuSet = 0;
+	}
+    }
+    if (cpuSet) {

and this if is skipped,

+        if (first == last)
+            virBufferAsprintf(buf, "%d,", first);
+        else
+            virBufferAsprintf(buf, "%d-%d,", first, last);
+    }
+    /* Remove the trailing comma */
+    return virBufferTruncate(buf, 1);

meaning that nothing was appended to buf, and you are now stripping unknown text, rather than a comma you just added. Do we need a sanity check to ensure that the cpumask specifies at least one cpu? And if so, would that mask be better here, or up front at the xml parsing time?

+static int
+qemuBuildNumaArgStr(const virDomainDefPtr def, virCommandPtr cmd)
+    int i;
+    char *node;
+    virBuffer buf = VIR_BUFFER_INITIALIZER;
+    for (i = 0; i<  def->cpu->ncells; i++) {
+        virCommandAddArg(cmd, "-numa");
+        virBufferAsprintf(&buf, "%s", "node");

More efficient as virBufferAddLit(&buf, "node"), or...

+        virBufferAsprintf(&buf, ",nodeid=%d", def->cpu->cells[i].cellid);

merge these two into a single:

virBufferAsprintf(&buf, "node,nodeid=%d", ...);

+        virBufferAsprintf(&buf, ",cpus=");

Again, with no % in the format string, it is more efficient to use virBufferAddLit.

+        if (qemuBuildNumaCPUArgStr(def->cpu->cells[i].cpumask,&buf))

Generally, we prefer an explicit < 0 comparison when checking for failure.

+            goto error;
+        virBufferAsprintf(&buf, ",mems=%d", def->cpu->cells[i].mem);

Why do we need to bother with stripping a trailing comma in qemuBuildNumaCPUArgStr, if we will just be adding a comma back again here as the very next statement? You could skip all the hassle of adding virBufferTruncate by just transferring the comma out of this statement and into qemuBuildNumaCPUArgStr (that said, I still think virBufferTruncate will be a useful addition in other contexts).

+        if (virBufferError(&buf))
+            goto error;
+        node = virBufferContentAndReset(&buf);
+        virCommandAddArg(cmd, node);
+        VIR_FREE(node);

It's more efficient to replace these five lines with one:

virCommandAddArgBuffer(cmd, &buf);

@@ -3414,6 +3482,9 @@ qemuBuildCommandLine(virConnectPtr conn,
      virCommandAddArg(cmd, smp);

+    if (def->cpu&&  def->cpu->ncells&&  qemuBuildNumaArgStr(def, cmd))

Again, explicit < 0 check when looking for errors.

+<topology sockets="2" cores="4" threads="2"/>
+<cell cpus="0-7" mems="109550"/>
+<cell cpus="8-15" mems="109550"/>

Of course, this will need tweaking to match any XML changes made in 1/3, but thanks for adding test cases!

Overall, I think we'll need a v3 (you may want to use git send-email --subject-prefix=PATCHv3; it wasn't very clear from the subject line that this was already a v2 series), but I like where it's heading.

Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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