[RFC,03/26] machine: Add auxcpus=N suboption to -smp

Commit Message

Dov Murik March 2, 2021, 8:47 p.m. UTC

Add a notion of auxiliary vcpus to CpuTopology, which will allow to
designate a few vcpus (normally 1) to helper tasks not related to main
guest VM execution.

Example usage for starting a 4-vcpu guest, of which 1 vcpu is marked as
auxiliary:

    qemu-system-x86_64 -smp 4,auxcpus=1 ...

Signed-off-by: Dov Murik <[e-mail]>
---
 include/hw/boards.h | 1 +
 hw/core/machine.c   | 7 +++++++
 hw/i386/pc.c        | 7 +++++++
 softmmu/vl.c        | 3 +++
 4 files changed, 18 insertions(+)

Patch

diff --git a/include/hw/boards.h b/include/hw/boards.h
index a46dfe5d1a..7ee5c73510 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -246,6 +246,7 @@  typedef struct CpuTopology {
     unsigned int threads;
     unsigned int sockets;
     unsigned int max_cpus;
+    unsigned int aux_cpus;
 } CpuTopology;
 
 /**
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 970046f438..08ea2cedea 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -722,6 +722,7 @@  static void smp_parse(MachineState *ms, QemuOpts *opts)
         unsigned sockets = qemu_opt_get_number(opts, "sockets", 0);
         unsigned cores   = qemu_opt_get_number(opts, "cores", 0);
         unsigned threads = qemu_opt_get_number(opts, "threads", 0);
+        unsigned aux_cpus = qemu_opt_get_number(opts, "auxcpus", 0);
 
         /* compute missing values, prefer sockets over cores over threads */
         if (cpus == 0 || sockets == 0) {
@@ -767,10 +768,16 @@  static void smp_parse(MachineState *ms, QemuOpts *opts)
             exit(1);
         }
 
+        if (aux_cpus >= ms->smp.max_cpus) {
+            error_report("auxcpus must be lower than max_cpus");
+            exit(1);
+        }
+
         ms->smp.cpus = cpus;
         ms->smp.cores = cores;
         ms->smp.threads = threads;
         ms->smp.sockets = sockets;
+        ms->smp.aux_cpus = aux_cpus;
     }
 
     if (ms->smp.cpus > 1) {
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 8aa85dec54..95d3769842 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -718,6 +718,7 @@  void pc_smp_parse(MachineState *ms, QemuOpts *opts)
         unsigned dies = qemu_opt_get_number(opts, "dies", 1);
         unsigned cores   = qemu_opt_get_number(opts, "cores", 0);
         unsigned threads = qemu_opt_get_number(opts, "threads", 0);
+        unsigned aux_cpus = qemu_opt_get_number(opts, "auxcpus", 0);
 
         /* compute missing values, prefer sockets over cores over threads */
         if (cpus == 0 || sockets == 0) {
@@ -763,10 +764,16 @@  void pc_smp_parse(MachineState *ms, QemuOpts *opts)
             exit(1);
         }
 
+        if (aux_cpus >= ms->smp.max_cpus) {
+            error_report("auxcpus must be lower than max_cpus");
+            exit(1);
+        }
+
         ms->smp.cpus = cpus;
         ms->smp.cores = cores;
         ms->smp.threads = threads;
         ms->smp.sockets = sockets;
+        ms->smp.aux_cpus = aux_cpus;
         x86ms->smp_dies = dies;
     }
 
diff --git a/softmmu/vl.c b/softmmu/vl.c
index b219ce1f35..96f0ff8111 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -720,6 +720,9 @@  static QemuOptsList qemu_smp_opts = {
         }, {
             .name = "maxcpus",
             .type = QEMU_OPT_NUMBER,
+        }, {
+            .name = "auxcpus",
+            .type = QEMU_OPT_NUMBER,
         },
         { /*End of list */ }
     },