Re: [Qemu-devel] [PATCH] Fixes related to processing of qemu's -numa option

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On 6/18/2012 1:29 PM, Eduardo Habkost wrote:
On Sun, Jun 17, 2012 at 01:12:31PM -0700, Chegu Vinod wrote:
The -numa option to qemu is used to create [fake] numa nodes
and expose them to the guest OS instance.

There are a couple of issues with the -numa option:

a) Max VCPU's that can be specified for a guest while using
    the qemu's -numa option is 64. Due to a typecasting issue
    when the number of VCPUs is>  32 the VCPUs don't show up
    under the specified [fake] numa nodes.

b) KVM currently has support for 160VCPUs per guest. The
    qemu's -numa option has only support for upto 64VCPUs
    per guest.

This patch addresses these two issues. [ Note: This
patch has been verified by Eduardo Habkost ].
I was going to add a Tested-by line, but this patch breaks the automatic
round-robin assignment when no CPU is added to any node on the
command-line.

Pl. see below.

Additional questions below:

[...]
diff --git a/cpus.c b/cpus.c
index b182b3d..f9cee60 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1145,7 +1145,7 @@ void set_numa_modes(void)

      for (env = first_cpu; env != NULL; env = env->next_cpu) {
          for (i = 0; i<  nb_numa_nodes; i++) {
-            if (node_cpumask[i]&  (1<<  env->cpu_index)) {
+            if (CPU_ISSET_S(env->cpu_index, cpumask_size, node_cpumask[i])) {
                  env->numa_node = i;
              }
          }
diff --git a/hw/pc.c b/hw/pc.c
index 8368701..f0c3665 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -639,7 +639,7 @@ static void *bochs_bios_init(void)
      numa_fw_cfg[0] = cpu_to_le64(nb_numa_nodes);
      for (i = 0; i<  max_cpus; i++) {
          for (j = 0; j<  nb_numa_nodes; j++) {
-            if (node_cpumask[j]&  (1<<  i)) {
+            if (CPU_ISSET_S(i, cpumask_size, node_cpumask[j])) {
                  numa_fw_cfg[i + 1] = cpu_to_le64(j);
                  break;
              }
diff --git a/sysemu.h b/sysemu.h
index bc2c788..6e4d342 100644
--- a/sysemu.h
+++ b/sysemu.h
@@ -9,6 +9,7 @@
  #include "qapi-types.h"
  #include "notify.h"
  #include "main-loop.h"
+#include<sched.h>

  /* vl.c */

@@ -133,9 +134,11 @@ extern uint8_t qemu_extra_params_fw[2];
  extern QEMUClock *rtc_clock;

  #define MAX_NODES 64
+#define KVM_MAX_VCPUS 254
Do we really need this constant? Why not just use max_cpus when
allocating the CPU sets, instead?

Hmm.... I had thought about this earlier too max_cpus was not getting set at the point where the allocations were being done. I have now moved that code to a bit later and switched to using
max_cpus.



  extern int nb_numa_nodes;
  extern uint64_t node_mem[MAX_NODES];
-extern uint64_t node_cpumask[MAX_NODES];
+extern cpu_set_t *node_cpumask[MAX_NODES];
+extern size_t cpumask_size;

  #define MAX_OPTION_ROMS 16
  typedef struct QEMUOptionRom {
diff --git a/vl.c b/vl.c
index 204d85b..1906412 100644
--- a/vl.c
+++ b/vl.c
@@ -28,6 +28,7 @@
  #include<errno.h>
  #include<sys/time.h>
  #include<zlib.h>
+#include<sched.h>

  /* Needed early for CONFIG_BSD etc. */
  #include "config-host.h"
@@ -240,7 +241,8 @@ QTAILQ_HEAD(, FWBootEntry) fw_boot_order = QTAILQ_HEAD_INITIALIZER(fw_boot_order

  int nb_numa_nodes;
  uint64_t node_mem[MAX_NODES];
-uint64_t node_cpumask[MAX_NODES];
+cpu_set_t *node_cpumask[MAX_NODES];
+size_t cpumask_size;

  uint8_t qemu_uuid[16];

@@ -950,6 +952,9 @@ static void numa_add(const char *optarg)
      char *endptr;
      unsigned long long value, endvalue;
      int nodenr;
+    int i;
+
+    value = endvalue = 0;

      optarg = get_opt_name(option, 128, optarg, ',') + 1;
      if (!strcmp(option, "node")) {
@@ -970,27 +975,17 @@ static void numa_add(const char *optarg)
              }
              node_mem[nodenr] = sval;
          }
-        if (get_param_value(option, 128, "cpus", optarg) == 0) {
-            node_cpumask[nodenr] = 0;
-        } else {
+        if (get_param_value(option, 128, "cpus", optarg) != 0) {
              value = strtoull(option,&endptr, 10);
-            if (value>= 64) {
-                value = 63;
-                fprintf(stderr, "only 64 CPUs in NUMA mode supported.\n");
+            if (*endptr == '-') {
+                endvalue = strtoull(endptr+1,&endptr, 10);
              } else {
-                if (*endptr == '-') {
-                    endvalue = strtoull(endptr+1,&endptr, 10);
-                    if (endvalue>= 63) {
-                        endvalue = 62;
-                        fprintf(stderr,
-                            "only 63 CPUs in NUMA mode supported.\n");
-                    }
-                    value = (2ULL<<  endvalue) - (1ULL<<  value);
-                } else {
-                    value = 1ULL<<  value;
-                }
+                endvalue = value;
+            }
+
+            for (i = value; i<= endvalue; ++i) {
+                CPU_SET_S(i, cpumask_size, node_cpumask[nodenr]);
What if endvalue is larger than the cpu mask size we allocated?

I can add a check (endvalue >= max_cpus) and print an error.
Should we force set the endvalue to max_cpus-1 in that case ?




              }
-            node_cpumask[nodenr] = value;
          }
          nb_numa_nodes++;
      }
@@ -2331,7 +2326,9 @@ int main(int argc, char **argv, char **envp)

      for (i = 0; i<  MAX_NODES; i++) {
          node_mem[i] = 0;
-        node_cpumask[i] = 0;
+        node_cpumask[i] = CPU_ALLOC(KVM_MAX_VCPUS);
+        cpumask_size = CPU_ALLOC_SIZE(KVM_MAX_VCPUS);
+        CPU_ZERO_S(cpumask_size, node_cpumask[i]);
      }

      nb_numa_nodes = 0;
@@ -3465,8 +3462,9 @@ int main(int argc, char **argv, char **envp)
          }

          for (i = 0; i<  nb_numa_nodes; i++) {
-            if (node_cpumask[i] != 0)
+            if (node_cpumask[i] != NULL) {
This will be true for every node (as you preallocate all the CPU
sets in the beginning), so the loop will always end with i==0, in turn
unconditionally disabling the round-robin CPU assignment code below.
You can use CPU_COUNT_S, instead.

Argh... I should have tested this. My bad ! Thanks for catching this. I made the change and tested it and its doing the round-robin assignment now.

Will post the next version of the patch soon.

Thanks for your feedback.
Vinod

                  break;
+            }
          }
          /* assigning the VCPUs round-robin is easier to implement, guest OSes
           * must cope with this anyway, because there are BIOSes out there in
@@ -3474,7 +3472,7 @@ int main(int argc, char **argv, char **envp)
           */
          if (i == nb_numa_nodes) {
              for (i = 0; i<  max_cpus; i++) {
-                node_cpumask[i % nb_numa_nodes] |= 1<<  i;
+                CPU_SET_S(i, cpumask_size, node_cpumask[i % nb_numa_nodes]);
              }
          }
      }
--
1.7.1


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