Re: [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp p

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Re: [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp p

From:	wangyanan (Y)
Subject:	Re: [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp parsing since 6.2
Date:	Mon, 16 Aug 2021 11:02:57 +0800
User-agent:	Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0

On 2021/8/14 0:30, Pankaj Gupta wrote:

In the real SMP hardware topology world, it's much more likely that
we have high cores-per-socket counts and few sockets totally. While
the current preference of sockets over cores in smp parsing results
in a virtual cpu topology with low cores-per-sockets counts and a
large number of sockets, which is just contrary to the real world.

Given that it is better to make the virtual cpu topology be more
reflective of the real world and also for the sake of compatibility,
we start to prefer cores over sockets over threads in smp parsing
since machine type 6.2 for different arches.

In this patch, a boolean "smp_prefer_sockets" is added, and we only
enable the old preference on older machines and enable the new one
since type 6.2 for all arches by using the machine compat mechanism.

Suggested-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
---
  hw/arm/virt.c              |  1 +
  hw/core/machine.c          | 35 ++++++++++++++++++++++++++---------
  hw/i386/pc.c               | 35 ++++++++++++++++++++++++++---------
  hw/i386/pc_piix.c          |  1 +
  hw/i386/pc_q35.c           |  1 +
  hw/ppc/spapr.c             |  1 +
  hw/s390x/s390-virtio-ccw.c |  1 +
  include/hw/boards.h        |  1 +
  qemu-options.hx            |  3 ++-
  9 files changed, 60 insertions(+), 19 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 01165f7f53..7babea40dc 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -2797,6 +2797,7 @@ static void virt_machine_6_1_options(MachineClass *mc)
  {
      virt_machine_6_2_options(mc);
      compat_props_add(mc->compat_props, hw_compat_6_1, hw_compat_6_1_len);
+    mc->smp_prefer_sockets = true;

Will this be set for virt_machine_6_2_?

Hi,

We hope to start to assume cores over sockets on virt_6_2 machines
and the later, and keep the old style of assuming sockets over cores
on virt_6_1 machines and the older. Is there any concern here?

Thanks,
Yanan

  }
  DEFINE_VIRT_MACHINE(6, 1)

diff --git a/hw/core/machine.c b/hw/core/machine.c
index bdce80df32..15b41c52e8 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -748,6 +748,7 @@ void machine_set_cpu_numa_node(MachineState *machine,

  static void smp_parse(MachineState *ms, SMPConfiguration *config, Error 
**errp)
  {
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
      unsigned cpus    = config->has_cpus ? config->cpus : 0;
      unsigned sockets = config->has_sockets ? config->sockets : 0;
      unsigned cores   = config->has_cores ? config->cores : 0;
@@ -759,7 +760,7 @@ static void smp_parse(MachineState *ms, SMPConfiguration 
*config, Error **errp)
          return;
      }

-    /* compute missing values, prefer sockets over cores over threads */
+    /* compute missing values based on the provided ones */
      if (cpus == 0 && maxcpus == 0) {
          sockets = sockets > 0 ? sockets : 1;
          cores = cores > 0 ? cores : 1;
@@ -767,14 +768,30 @@ static void smp_parse(MachineState *ms, SMPConfiguration 
*config, Error **errp)
      } else {
          maxcpus = maxcpus > 0 ? maxcpus : cpus;

-        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) {
+        if (mc->smp_prefer_sockets) {
+            /* prefer sockets over cores before 6.2 */
+            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 {
+            /* prefer cores over sockets since 6.2 */
+            if (cores == 0) {
+                sockets = sockets > 0 ? sockets : 1;
+                threads = threads > 0 ? threads : 1;
+                cores = maxcpus / (sockets * threads);
+            } else if (sockets == 0) {
+                threads = threads > 0 ? threads : 1;
+                sockets = maxcpus / (cores * threads);
+            }
+        }
+
+        /* try to calculate omitted threads at last */
+        if (threads == 0) {
              threads = maxcpus / (sockets * cores);
          }
      }
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index afd8b9c283..4b05ff7160 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -717,6 +717,7 @@ void pc_acpi_smi_interrupt(void *opaque, int irq, int level)
   */
  static void pc_smp_parse(MachineState *ms, SMPConfiguration *config, Error 
**errp)
  {
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
      unsigned cpus    = config->has_cpus ? config->cpus : 0;
      unsigned sockets = config->has_sockets ? config->sockets : 0;
      unsigned dies    = config->has_dies ? config->dies : 0;
@@ -727,7 +728,7 @@ static void pc_smp_parse(MachineState *ms, SMPConfiguration 
*config, Error **err
      /* directly default dies to 1 if it's omitted */
      dies = dies > 0 ? dies : 1;

-    /* compute missing values, prefer sockets over cores over threads */
+    /* compute missing values based on the provided ones */
      if (cpus == 0 && maxcpus == 0) {
          sockets = sockets > 0 ? sockets : 1;
          cores = cores > 0 ? cores : 1;
@@ -735,14 +736,30 @@ static void pc_smp_parse(MachineState *ms, 
SMPConfiguration *config, Error **err
      } else {
          maxcpus = maxcpus > 0 ? maxcpus : cpus;

-        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) {
+        if (mc->smp_prefer_sockets) {
+            /* prefer sockets over cores before 6.2 */
+            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 {
+            /* prefer cores over sockets since 6.2 */
+            if (cores == 0) {
+                sockets = sockets > 0 ? sockets : 1;
+                threads = threads > 0 ? threads : 1;
+                cores = maxcpus / (sockets * dies * threads);
+            } else if (sockets == 0) {
+                threads = threads > 0 ? threads : 1;
+                sockets = maxcpus / (dies * cores * threads);
+            }
+        }
+
+        /* try to calculate omitted threads at last */
+        if (threads == 0) {
              threads = maxcpus / (sockets * dies * cores);
          }
      }
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index fd5c2277f2..9b811fc6ca 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -432,6 +432,7 @@ static void pc_i440fx_6_1_machine_options(MachineClass *m)
      m->is_default = false;
      compat_props_add(m->compat_props, hw_compat_6_1, hw_compat_6_1_len);
      compat_props_add(m->compat_props, pc_compat_6_1, pc_compat_6_1_len);
+    m->smp_prefer_sockets = true;
  }

  DEFINE_I440FX_MACHINE(v6_1, "pc-i440fx-6.1", NULL,
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index b45903b15e..88efb7fde4 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -372,6 +372,7 @@ static void pc_q35_6_1_machine_options(MachineClass *m)
      m->alias = NULL;
      compat_props_add(m->compat_props, hw_compat_6_1, hw_compat_6_1_len);
      compat_props_add(m->compat_props, pc_compat_6_1, pc_compat_6_1_len);
+    m->smp_prefer_sockets = true;
  }

  DEFINE_Q35_MACHINE(v6_1, "pc-q35-6.1", NULL,
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index d39fd4e644..a481fade51 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -4702,6 +4702,7 @@ static void spapr_machine_6_1_class_options(MachineClass 
*mc)
  {
      spapr_machine_6_2_class_options(mc);
      compat_props_add(mc->compat_props, hw_compat_6_1, hw_compat_6_1_len);
+    mc->smp_prefer_sockets = true;
  }

  DEFINE_SPAPR_MACHINE(6_1, "6.1", false);
diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 4d25278cf2..b40e647883 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -809,6 +809,7 @@ static void ccw_machine_6_1_class_options(MachineClass *mc)
  {
      ccw_machine_6_2_class_options(mc);
      compat_props_add(mc->compat_props, hw_compat_6_1, hw_compat_6_1_len);
+    mc->smp_prefer_sockets = true;
  }
  DEFINE_CCW_MACHINE(6_1, "6.1", false);

diff --git a/include/hw/boards.h b/include/hw/boards.h
index 463a5514f9..2ae039b74f 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -247,6 +247,7 @@ struct MachineClass {
      bool nvdimm_supported;
      bool numa_mem_supported;
      bool auto_enable_numa;
+    bool smp_prefer_sockets;
      const char *default_ram_id;

      HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
diff --git a/qemu-options.hx b/qemu-options.hx
index 06f819177e..451d2cd817 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -238,7 +238,8 @@ SRST
      Historically preference was given to the coarsest topology parameters
      when computing missing values (ie sockets preferred over cores, which
      were preferred over threads), however, this behaviour is considered
-    liable to change.
+    liable to change. Prior to 6.2 the preference was sockets over cores
+    over threads. Since 6.2 the preference is cores over sockets over threads.
  ERST

  DEF("numa", HAS_ARG, QEMU_OPTION_numa,
--
2.19.1

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[PATCH for-6.2 v5 00/14] machine: smp parsing fixes and improvement, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 02/14] machine: Uniformly use maxcpus to calculate the omitted parameters, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 04/14] machine: Improve the error reporting of smp parsing, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 01/14] machine: Minor refactor/cleanup for the smp parsers, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 03/14] machine: Set the value of cpus to match maxcpus if it's omitted, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp parsing since 6.2, Yanan Wang, 2021/08/12
  - Re: [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp parsing since 6.2, Pankaj Gupta, 2021/08/13
    - Re: [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp parsing since 6.2, wangyanan (Y) <=
    - Re: [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp parsing since 6.2, Pankaj Gupta, 2021/08/16
  - Re: [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp parsing since 6.2, Pankaj Gupta, 2021/08/16
    - Re: [PATCH for-6.2 v5 06/14] machine: Prefer cores over sockets in smp parsing since 6.2, wangyanan (Y), 2021/08/16
- [PATCH for-6.2 v5 07/14] machine: Use ms instead of global current_machine in sanity-check, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 09/14] machine: Make smp_parse generic enough for all arches, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 05/14] hw: Add compat machines for 6.2, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 12/14] machine: Put all sanity-check in the generic SMP parser, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 10/14] machine: Remove smp_parse callback from MachineClass, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 13/14] machine: Split out the smp parsing code, Yanan Wang, 2021/08/12
- [PATCH for-6.2 v5 08/14] machine: Tweak the order of topology members in struct CpuTopology, Yanan Wang, 2021/08/12

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