Re: [Xen-devel] [Qemu-devel] [PATCH v5 2/3] pc & q35: Add new machine opt max-ram-below-4g

[Igor Mammedov <imammedo@xxxxxxxxxx>]

On Mon, 09 Jun 2014 18:10:27 +0300
Marcel Apfelbaum <marcel.a@xxxxxxxxxx> wrote:

> Hi,
> 
> On Mon, 2014-06-09 at 17:38 +0300, Michael S. Tsirkin wrote:
> > On Mon, Jun 09, 2014 at 10:20:57AM -0400, Don Slutz wrote:
> > > On 06/08/14 11:40, Michael S. Tsirkin wrote:
> > > >On Fri, Jun 06, 2014 at 01:52:05PM -0400, Don Slutz wrote:
> > > >>This is a pc & q35 only machine opt.  One use is to allow for more
> > > >>ram in a 32bit guest for example:
> > > >>
> > > >>-machine pc,max-ram-below-4g=3.75G
> > > >>
> > > >>If you add enough PCI devices then all mmio for them will not fit
> > > >>below 4G which may not be the layout the user wanted. This allows
> > > >>you to increase the below 4G address space that PCI devices can use
> > > >>(aka decrease ram below 4G) and therefore in more cases not have any
> > > >>mmio that is above 4G.
> > > >>
> > > >>For example using "-machine pc,max-ram-below-4g=2G" on the command
> > > >>line will limit the amount of ram that is below 4G to 2G.
> > > >>
> > > >>Signed-off-by: Don Slutz <dslutz@xxxxxxxxxxx>
> > > >>---
> > > >>v5:
> > > >>   Re-work based on:
> > > >>
> > > >>   https://github.com/imammedo/qemu/commits/memory-hotplug-v11
> > > >>
> > > >>
> > > >>  hw/i386/pc.c         | 38 ++++++++++++++++++++++++++++++++++++++
> > > >>  hw/i386/pc_piix.c    | 15 ++++++++++++---
> > > >>  hw/i386/pc_q35.c     | 15 ++++++++++++---
> > > >>  include/hw/i386/pc.h |  3 +++
> > > >>  vl.c                 |  4 ++++
> > > >>  5 files changed, 69 insertions(+), 6 deletions(-)
> > > >>
> > > >>diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > >>index 7cdba10..bccb746 100644
> > > >>--- a/hw/i386/pc.c
> > > >>+++ b/hw/i386/pc.c
> > > >>@@ -1644,11 +1644,49 @@ 
> > > >>pc_machine_get_hotplug_memory_region_size(Object *obj, Visitor *v, void 
> > > >>*opaque,
> > > >>      visit_type_int(v, &value, name, errp);
> > > >>  }
> > > >>+static void pc_machine_get_max_ram_below_4g(Object *obj, Visitor *v,
> > > >>+                                         void *opaque, const char 
> > > >>*name,
> > > >>+                                         Error **errp)
> > > >>+{
> > > >>+    PCMachineState *pcms = PC_MACHINE(obj);
> > > >>+    uint64_t value = pcms->max_ram_below_4g;
> > > >>+
> > > >>+    visit_type_size(v, &value, name, errp);
> > > >>+}
> > > >>+
> > > >>+static void pc_machine_set_max_ram_below_4g(Object *obj, Visitor *v,
> > > >>+                                         void *opaque, const char 
> > > >>*name,
> > > >>+                                         Error **errp)
> > > >>+{
> > > >>+    PCMachineState *pcms = PC_MACHINE(obj);
> > > >>+    Error *error = NULL;
> > > >>+    uint64_t value;
> > > >>+
> > > >>+    visit_type_size(v, &value, name, &error);
> > > >>+    if (error) {
> > > >>+        error_propagate(errp, error);
> > > >>+        return;
> > > >>+    }
> > > >>+    if (value > (1ULL << 32)) {
> > > >>+        error_set(&error, ERROR_CLASS_GENERIC_ERROR,
> > > >>+                  "Machine option 'max-ram-below-4g=%"PRIu64
> > > >>+                  "' expects size less then or equal to 4G", value);
> > > >less than
> > > 
> > > But the test is greater then.  So "not greater then" is "less then or 
> > > equal".
> > > Or did you want the test changed?
> > 
> > No, just correcting English: less than, not less then :)
> > 
> > > >>+        error_propagate(errp, error);
> > > >>+        return;
> > > >>+    }
> > > >>+
> > > >>+    pcms->max_ram_below_4g = value;
> > > >>+}
> > > >>+
> > > >>  static void pc_machine_initfn(Object *obj)
> > > >>  {
> > > >>      object_property_add(obj, PC_MACHINE_MEMHP_REGION_SIZE, "int",
> > > >>                          pc_machine_get_hotplug_memory_region_size,
> > > >>                          NULL, NULL, NULL, NULL);
> > > >>+    object_property_add(obj, PC_MACHINE_MAX_RAM_BELOW_4G,  "size",
> > > >>+                        pc_machine_get_max_ram_below_4g,
> > > >>+                        pc_machine_set_max_ram_below_4g,
> > > >>+                        NULL, NULL, NULL);
> Maybe you can add here a sane default and avoid comparison with 0
> any time you use it.
+1

> If you think you need value per machine type, you can add it to
> compat props. I don't see how is related, so you may not want to do so.
Using compat_props would be great however does compat_props work for machine
type itself already?

> 
> > > >>  }
> > > >>  static void pc_machine_class_init(ObjectClass *oc, void *data)
> > > >>diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > > >>index 40f6eaf..25f4727 100644
> > > >>--- a/hw/i386/pc_piix.c
> > > >>+++ b/hw/i386/pc_piix.c
> > > >>@@ -98,6 +98,13 @@ static void pc_init1(MachineState *machine,
> > > >>      DeviceState *icc_bridge;
> > > >>      FWCfgState *fw_cfg = NULL;
> > > >>      PcGuestInfo *guest_info;
> > > >>+    Object *mo = qdev_get_machine();
> > > >>+    PCMachineState *pcms = PC_MACHINE(mo);
> > > >>+    ram_addr_t lowmem = 0xe0000000;
> > > >>+
> > > >>+    if (pcms && pcms->max_ram_below_4g) {
> From my QOM understanding, max_ram_below_4g is a private field,
> so it not should be used directly.
> You can use QOMs object_property_get or add a pc_machine wrapper
> for getting/setting the field.
pc_init1() is sort of private function of PCMachine, so there is no much
point to use verbose getters/setters internally unless there is checks behind
setter.

> 
> > > >Is pcms ever NULL? If yes why?
> > > 
> > > Not that I know of.  I would be happy to convert this to an assert(pcms).
> > 
> > In fact, PC_MACHINE already includes an assert doesn't it?
> > So no need to check it everywhere.
> 
> +1. No need for assert here. Is already done by OBJECT_CHECK.
> 
> Hope I helped,
> Marcel
> 
> > 
> > > >>+        lowmem = pcms->max_ram_below_4g;
> > > >>+    }
> > > >>      /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO 
> > > >> memory).
> > > >>       * If it doesn't, we need to split it in chunks below and above 
> > > >> 4G.
> > > >>@@ -106,8 +113,10 @@ static void pc_init1(MachineState *machine,
> > > >>       * For old machine types, use whatever split we used historically 
> > > >> to avoid
> > > >>       * breaking migration.
> > > >>       */
> > > >>-    if (machine->ram_size >= 0xe0000000) {
> > > >>-        ram_addr_t lowmem = gigabyte_align ? 0xc0000000 : 0xe0000000;
> > > >>+    if (machine->ram_size >= lowmem) {
> > > >>+        if (!(pcms && pcms->max_ram_below_4g) && gigabyte_align) {
> > > >>+            lowmem = 0xc0000000;
> > > >>+        }
> > > >>          above_4g_mem_size = machine->ram_size - lowmem;
> > > >>          below_4g_mem_size = lowmem;
> > > >>      } else {
> > > >
> > > >So why do we need gigabyte_align anymore?
> > > 
> > > Because of qemu 2.0 and the user is not required to specify this option.
> > > 
> > > >Can't we set property to 0xc0000000 by default, and
> > > >override for old machine types?
> > > 
> > > There is a strange compatibility part here.  Since this code includes 
> > > ram_size (see:
> > > 
> > > http://lists.gnu.org/archive/html/qemu-devel/2014-02/msg05146.html
> > > 
> > > ) and xen has a different default.
> > > 
> > 
> > So instead of default 0, it would be preferable to set the default to the
> > actual value, and let user override it.
> > 
> > Or if that's too hard, set max_ram_below_4g instead of setting
> > gigabyte_align. gigabyte_align switches everywhere is messy
> > enough, adding max_ram_below_4g into mix is just too messy.
> > 
> > 
> > 
> > > >Also, a value that isn't a multiple of 1G will lead to bad
> > > >performance for large machines which do have above_4g_mem_size.
> > > >Let's detect and print a warning.
> > > 
> > > Will Do.
> > > 
> > >    -Don Slutz
> > > 
> > > >
> > > >
> > > >>@@ -122,7 +131,7 @@ static void pc_init1(MachineState *machine,
> > > >>      }
> > > >>      icc_bridge = qdev_create(NULL, TYPE_ICC_BRIDGE);
> > > >>-    object_property_add_child(qdev_get_machine(), "icc-bridge",
> > > >>+    object_property_add_child(mo, "icc-bridge",
> > > >>                                OBJECT(icc_bridge), NULL);
> > > >>      pc_cpus_init(machine->cpu_model, icc_bridge);
> > > >>diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> > > >>index e28ce40..155cdf1 100644
> > > >>--- a/hw/i386/pc_q35.c
> > > >>+++ b/hw/i386/pc_q35.c
> > > >>@@ -85,6 +85,13 @@ static void pc_q35_init(MachineState *machine)
> > > >>      PCIDevice *ahci;
> > > >>      DeviceState *icc_bridge;
> > > >>      PcGuestInfo *guest_info;
> > > >>+    Object *mo = qdev_get_machine();
> > > >>+    PCMachineState *pcms = PC_MACHINE(mo);
> > > >>+    ram_addr_t lowmem = 0xb0000000;
> > > >>+
> > > >>+    if (pcms && pcms->max_ram_below_4g) {
> > > >>+        lowmem = pcms->max_ram_below_4g;
> > > >>+    }
> > > >>      /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO 
> > > >> memory
> > > >>       * and 256 Mbytes for PCI Express Enhanced Configuration Access 
> > > >> Mapping
> > > >>@@ -95,8 +102,10 @@ static void pc_q35_init(MachineState *machine)
> > > >>       * For old machine types, use whatever split we used historically 
> > > >> to avoid
> > > >>       * breaking migration.
> > > >>       */
> > > >>-    if (machine->ram_size >= 0xb0000000) {
> > > >>-        ram_addr_t lowmem = gigabyte_align ? 0x80000000 : 0xb0000000;
> > > >>+    if (machine->ram_size >= lowmem) {
> > > >>+        if (!(pcms && pcms->max_ram_below_4g) && gigabyte_align) {
> > > >>+            lowmem = 0x800000000;
> > > >>+        }
> > > >>          above_4g_mem_size = machine->ram_size - lowmem;
> > > >>          below_4g_mem_size = lowmem;
> > > >>      } else {
> > > >>@@ -111,7 +120,7 @@ static void pc_q35_init(MachineState *machine)
> > > >>      }
> > > >>      icc_bridge = qdev_create(NULL, TYPE_ICC_BRIDGE);
> > > >>-    object_property_add_child(qdev_get_machine(), "icc-bridge",
> > > >>+    object_property_add_child(mo, "icc-bridge",
> > > >>                                OBJECT(icc_bridge), NULL);
> > > >>      pc_cpus_init(machine->cpu_model, icc_bridge);
> > > >>diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > > >>index 19530bd..2d8b562 100644
> > > >>--- a/include/hw/i386/pc.h
> > > >>+++ b/include/hw/i386/pc.h
> > > >>@@ -32,10 +32,13 @@ struct PCMachineState {
> > > >>      MemoryRegion hotplug_memory;
> > > >>      HotplugHandler *acpi_dev;
> > > >>+
> > > >>+    uint64_t max_ram_below_4g;
> > > >>  };
> > > >>  #define PC_MACHINE_ACPI_DEVICE_PROP "acpi-device"
> > > >>  #define PC_MACHINE_MEMHP_REGION_SIZE "hotplug-memory-region-size"
> > > >>+#define PC_MACHINE_MAX_RAM_BELOW_4G "max-ram-below-4g"
> > > >>  /**
> > > >>   * PCMachineClass:
> > > >>diff --git a/vl.c b/vl.c
> > > >>index 5e77a27..cffb9c5 100644
> > > >>--- a/vl.c
> > > >>+++ b/vl.c
> > > >>@@ -382,6 +382,10 @@ static QemuOptsList qemu_machine_opts = {
> > > >>              .name = "kvm-type",
> > > >>              .type = QEMU_OPT_STRING,
> > > >>              .help = "Specifies the KVM virtualization mode (HV, PR)",
> > > >>+        },{
> > > >>+            .name = PC_MACHINE_MAX_RAM_BELOW_4G,
> > > >>+            .type = QEMU_OPT_SIZE,
> > > >>+            .help = "maximum ram below the 4G boundary (32bit 
> > > >>boundary)",
> > > >>          },
> > > >>          { /* End of list */ }
> > > >>      },
> > > >>-- 
> > > >>1.8.4
> > 
> 
> 
> 


-- 
Regards,
  Igor

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