Re: [RFC] allow multi-core guests: introduce cores= option to -cpu

Brian Jackson <iggy@xxxxxxxxxxx> · Fri, 03 Jul 2009 10:16:10 -0500

Andre Przywara wrote:
Hi,

currently SMP guests happen to see <n> vCPUs as <n> different sockets.
Some guests (Windows comes to mind) have license restrictions and refuse
to run on multi-socket machines.
So lets introduce a "cores=" parameter to the -cpu option to let the user
specify the number of _cores_ the guest should see.

This patch has not been tested with all corner cases, so I just want to
hear your comments whether
a) we need such an option  and
b) you like this particular approach.

Applying this qemu.git patch to qemu-kvm.git fixes Windows SMP boot on
some versions, I successfully tried up to -smp 16 -cpu host,cores=8 with
WindowsXP Pro.                  


Personally, I'd like to see it as an extra arg to the -smp option. We've 
seen too many people use -cpu incorrectly in #kvm, so we've gotten into 
the habit of telling people not to touch that option unless they know 
exactly what they are doing. Plus it seems odd to have to use -cpu foo 
when you just want more cpus, not a specific cpu.

--Iggy



Regards,
Andre.

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
---
 target-i386/cpu.h    |    1 +
 target-i386/helper.c |   26 ++++++++++++++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index 4a8608e..96fa471 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -657,6 +657,7 @@ typedef struct CPUX86State {
     uint32_t cpuid_ext3_features;
     uint32_t cpuid_apic_id;
     int cpuid_vendor_override;
+    int cpuid_cores;
 
     /* MTRRs */
     uint64_t mtrr_fixed[11];
diff --git a/target-i386/helper.c b/target-i386/helper.c
index 82e1ff1..9c54fb9 100644
--- a/target-i386/helper.c
+++ b/target-i386/helper.c
@@ -103,6 +103,7 @@ typedef struct x86_def_t {
     uint32_t xlevel;
     char model_id[48];
     int vendor_override;
+    int cores;
 } x86_def_t;
 
 #define I486_FEATURES (CPUID_FP87 | CPUID_VME | CPUID_PSE)
@@ -351,7 +352,7 @@ static int cpu_x86_find_by_name(x86_def_t *x86_cpu_def, const char *cpu_model)
     char *featurestr, *name = strtok(s, ",");
     uint32_t plus_features = 0, plus_ext_features = 0, plus_ext2_features = 0, plus_ext3_features = 0;
     uint32_t minus_features = 0, minus_ext_features = 0, minus_ext2_features = 0, minus_ext3_features = 0;
-    int family = -1, model = -1, stepping = -1;
+    int family = -1, model = -1, stepping = -1, cores = 1;
 
     def = NULL;
     for (i = 0; i < ARRAY_SIZE(x86_defs); i++) {
@@ -406,6 +407,14 @@ static int cpu_x86_find_by_name(x86_def_t *x86_cpu_def, const char *cpu_model)
                     goto error;
                 }
                 x86_cpu_def->stepping = stepping;
+            } else if (!strcmp(featurestr, "cores")) {
+                char *err;
+                cores = strtol(val, &err, 10);
+                if (!*val || *err || cores < 1 || cores > 0xff) {
+                    fprintf(stderr, "bad numerical value %s\n", val);
+                    goto error;
+                }
+                x86_cpu_def->cores = cores;
             } else if (!strcmp(featurestr, "vendor")) {
                 if (strlen(val) != 12) {
                     fprintf(stderr, "vendor string must be 12 chars long\n");
@@ -473,6 +482,7 @@ static int cpu_x86_register (CPUX86State *env, const char *cpu_model)
         env->cpuid_vendor3 = CPUID_VENDOR_INTEL_3;
     }
     env->cpuid_vendor_override = def->vendor_override;
+    env->cpuid_cores = def->cores;
     env->cpuid_level = def->level;
     if (def->family > 0x0f)
         env->cpuid_version = 0xf00 | ((def->family - 0x0f) << 20);
@@ -1562,9 +1572,14 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         break;
     case 1:
         *eax = env->cpuid_version;
-        *ebx = (env->cpuid_apic_id << 24) | 8 << 8; /* CLFLUSH size in quad words, Linux wants it. */
+        /* CLFLUSH size in quad words, Linux wants it. */
+        *ebx = (env->cpuid_apic_id << 24) | 8 << 8;
         *ecx = env->cpuid_ext_features;
         *edx = env->cpuid_features;
+        if (env->cpuid_cores > 1) {
+            *ebx |= env->cpuid_cores << 16;   /* LogicalProcessorCount */
+            *edx |= 1 << 28;    /* HTT bit */
+        }
         break;
     case 2:
         /* cache info: needed for Pentium Pro compatibility */
@@ -1642,6 +1657,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         *ecx = env->cpuid_ext3_features;
         *edx = env->cpuid_ext2_features;
 
+        if (env->cpuid_cores > 1) {
+            *ecx |= 1 << 1;    /* CmpLegacy bit */
+        }
+
         if (kvm_enabled()) {
             /* Nested SVM not yet supported in KVM */
             *ecx &= ~CPUID_EXT3_SVM;
@@ -1696,6 +1715,9 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         *ebx = 0;
         *ecx = 0;
         *edx = 0;
+        if (env->cpuid_cores > 1) {
+            *ecx |= env->cpuid_cores - 1;    /* NC: Number of CPU cores */
+        }
         break;
     case 0x8000000A:
         *eax = 0x00000001; /* SVM Revision */
--
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