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

["Michael S. Tsirkin" <mst@redhat.com>]

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@verizon.com>
> >>---
> >>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);
> >>  }
> >>  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) {
> >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.

> >>+        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