machine: Set the value of cpus to match maxcpus if it's omitted

Currently we directly calculate the omitted cpus based on the given
incomplete collection of parameters. This makes some cmdlines like:
  -smp maxcpus=16
  -smp sockets=2,maxcpus=16
  -smp sockets=2,dies=2,maxcpus=16
  -smp sockets=2,cores=4,maxcpus=16
not work. We should probably set the value of cpus to match maxcpus
if it's omitted, which will make above configs start to work.

So the calculation logic of cpus/maxcpus after this patch will be:
When both maxcpus and cpus are omitted, maxcpus will be calculated
from the given parameters and cpus will be set equal to maxcpus.
When only one of maxcpus and cpus is given then the omitted one
will be set to its counterpart's value. Both maxcpus and cpus may
be specified, but maxcpus must be equal to or greater than cpus.

Note: change in this patch won't affect any existing working cmdlines
but allows more incomplete configs to be valid.

Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210929025816.21076-6-wangyanan55@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 596e758133738bad8fe85d10de0138e606d4bea6..d8f458db601e936ffe7e75559f090764c40a49af 100644 (file)
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -760,25 +760,28 @@ static void smp_parse(MachineState *ms, SMPConfiguration *config, Error **errp)
     }
 
     /* compute missing values, prefer sockets over cores over threads */
-    maxcpus = maxcpus > 0 ? maxcpus : cpus;
-
-    if (cpus == 0) {
+    if (cpus == 0 && maxcpus == 0) {
         sockets = sockets > 0 ? sockets : 1;
         cores = cores > 0 ? cores : 1;
         threads = threads > 0 ? threads : 1;
-        cpus = sockets * cores * threads;
+    } else {
         maxcpus = maxcpus > 0 ? maxcpus : cpus;
-    } else if (sockets == 0) {
-        cores = cores > 0 ? cores : 1;
-        threads = threads > 0 ? threads : 1;
-        sockets = maxcpus / (cores * threads);
-    } else if (cores == 0) {
-        threads = threads > 0 ? threads : 1;
-        cores = maxcpus / (sockets * threads);
-    } else if (threads == 0) {
-        threads = maxcpus / (sockets * cores);
+
+        if (sockets == 0) {
+            cores = cores > 0 ? cores : 1;
+            threads = threads > 0 ? threads : 1;
+            sockets = maxcpus / (cores * threads);
+        } else if (cores == 0) {
+            threads = threads > 0 ? threads : 1;
+            cores = maxcpus / (sockets * threads);
+        } else if (threads == 0) {
+            threads = maxcpus / (sockets * cores);
+        }
     }
 
+    maxcpus = maxcpus > 0 ? maxcpus : sockets * cores * threads;
+    cpus = cpus > 0 ? cpus : maxcpus;
+
     if (sockets * cores * threads < cpus) {
         error_setg(errp, "cpu topology: "
                    "sockets (%u) * cores (%u) * threads (%u) < "

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index e37e84cc7bf0ea1033c9b00ac7bdeab5344208d8..f24a1d72ad14e4eb1865f33a5ce27c60d20eb16c 100644 (file)
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -727,25 +727,28 @@ static void pc_smp_parse(MachineState *ms, SMPConfiguration *config, Error **err
     dies = dies > 0 ? dies : 1;
 
     /* compute missing values, prefer sockets over cores over threads */
-    maxcpus = maxcpus > 0 ? maxcpus : cpus;
-
-    if (cpus == 0) {
+    if (cpus == 0 && maxcpus == 0) {
         sockets = sockets > 0 ? sockets : 1;
         cores = cores > 0 ? cores : 1;
         threads = threads > 0 ? threads : 1;
-        cpus = sockets * dies * cores * threads;
+    } else {
         maxcpus = maxcpus > 0 ? maxcpus : cpus;
-    } else if (sockets == 0) {
-        cores = cores > 0 ? cores : 1;
-        threads = threads > 0 ? threads : 1;
-        sockets = maxcpus / (dies * cores * threads);
-    } else if (cores == 0) {
-        threads = threads > 0 ? threads : 1;
-        cores = maxcpus / (sockets * dies * threads);
-    } else if (threads == 0) {
-        threads = maxcpus / (sockets * dies * cores);
+
+        if (sockets == 0) {
+            cores = cores > 0 ? cores : 1;
+            threads = threads > 0 ? threads : 1;
+            sockets = maxcpus / (dies * cores * threads);
+        } else if (cores == 0) {
+            threads = threads > 0 ? threads : 1;
+            cores = maxcpus / (sockets * dies * threads);
+        } else if (threads == 0) {
+            threads = maxcpus / (sockets * dies * cores);
+        }
     }
 
+    maxcpus = maxcpus > 0 ? maxcpus : sockets * dies * cores * threads;
+    cpus = cpus > 0 ? cpus : maxcpus;
+
     if (sockets * dies * cores * threads < cpus) {
         error_setg(errp, "cpu topology: "
                    "sockets (%u) * dies (%u) * cores (%u) * threads (%u) < "

diff --git a/qemu-options.hx b/qemu-options.hx
index 4a092a092ac68a0909c67aee1fdfbf5e50c555a9..2eac830fdb6867ceb17465f3a87a1c0de103c73d 100644 (file)
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -220,9 +220,14 @@ SRST
     Simulate a SMP system with '\ ``n``\ ' CPUs initially present on
     the machine type board. On boards supporting CPU hotplug, the optional
     '\ ``maxcpus``\ ' parameter can be set to enable further CPUs to be
-    added at runtime. If omitted the maximum number of CPUs will be
-    set to match the initial CPU count. Both parameters are subject to
-    an upper limit that is determined by the specific machine type chosen.
+    added at runtime. When both parameters are omitted, the maximum number
+    of CPUs will be calculated from the provided topology members and the
+    initial CPU count will match the maximum number. When only one of them
+    is given then the omitted one will be set to its counterpart's value.
+    Both parameters may be specified, but the maximum number of CPUs must
+    be equal to or greater than the initial CPU count. Both parameters are
+    subject to an upper limit that is determined by the specific machine
+    type chosen.
 
     To control reporting of CPU topology information, the number of sockets,
     dies per socket, cores per die, and threads per core can be specified.