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Re: [libvirt] [PATCH 4/5] qemu: Build command line for NUMA tuning




Hi Daniel,

How can we get NUMA-aligned memory and CPUs if we apply binding APIs after the process has already started? Might not all the memory already be allocated on the wrong nodes by then?

For expert users, what are the problems with starting qemu with an external numactl command (with --cpunodebind and --membind) to guarantee optimal alignment?

Alternatives?

- Bill


On 05/05/2011 11:21 AM, Daniel P. Berrange wrote:
On Thu, May 05, 2011 at 05:38:29PM +0800, Osier Yang wrote:
Just prepend numactl command line to qemu command line.
---
  src/qemu/qemu_command.c |   16 ++++++++++++++++
  1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 2205ed1..156fdfb 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -2762,7 +2762,23 @@ qemuBuildCommandLine(virConnectPtr conn,
          break;
      }

+#ifdef HAVE_NUMACTL
+    /* XXX: Logic here to build numactl commmand line need to be changed if
+     * more NUMA tuning related stuffs in future.
+     */
+    if (def->numatune.membind.nodeset) {
+        cmd = virCommandNewArgList(NUMACTL,
+                                   "-m",
+                                   def->numatune.membind.nodeset,
+                                   NULL);
+
+        virCommandAddArgList(cmd, emulator, "-S", NULL);
+    } else {
+        cmd = virCommandNewArgList(emulator, "-S", NULL);
+    }
+#else
      cmd = virCommandNewArgList(emulator, "-S", NULL);
+#endif

NACK to this approach. We should be using the libnuma APIs to set the
memory binding for the process directly, and not running the numactl
command.

Regards,
Daniel


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