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Re: [Qemu-devel] [PATCH V7 15/16] virtio-pci: increase the maximum numbe


From: Jason Wang
Subject: Re: [Qemu-devel] [PATCH V7 15/16] virtio-pci: increase the maximum number of virtqueues to 513
Date: Tue, 28 Apr 2015 11:12:10 +0800



On Mon, Apr 27, 2015 at 7:02 PM, Michael S. Tsirkin <address@hidden> wrote:
On Thu, Apr 23, 2015 at 02:21:48PM +0800, Jason Wang wrote:
This patch increases the maximum number of virtqueues for pci from 64 to 513. This will allow booting a virtio-net-pci device with 256 queue pairs on recent Linux host (which supports up to 256 tuntap queue pairs). To keep migration compatibility, 64 was kept for legacy machine types. This is because qemu in fact allows guest to probe the limit of
 virtqueues through trying to set queue_sel. So for legacy machine
 type, we should make sure setting queue_sel to more than 63 won't
 make effect.

This isn't a documented interface, and no guest that I know of does
this.  Accordingly, I think we should drop everything except the
hw/virtio/virtio-pci.c change.

We leave a chance for guest to use such undocumented behavior, so technically we'd better keep it and it maybe too late for us to fix if we find such a guest in the future. And consider keeping this compatibility was really not hard, so I suggest to include this.


 Cc: Paolo Bonzini <address@hidden>
 Cc: Richard Henderson <address@hidden>
 Cc: Michael S. Tsirkin <address@hidden>
 Cc: Alexander Graf <address@hidden>
 Cc: address@hidden
 Signed-off-by: Jason Wang <address@hidden>
 ---
  hw/i386/pc_piix.c      | 5 +++++
  hw/i386/pc_q35.c       | 5 +++++
  hw/ppc/spapr.c         | 5 +++++
  hw/virtio/virtio-pci.c | 6 +++++-
  4 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
 index 212e263..6e098ce 100644
 --- a/hw/i386/pc_piix.c
 +++ b/hw/i386/pc_piix.c
 @@ -49,6 +49,7 @@
  #include "hw/acpi/acpi.h"
  #include "cpu.h"
  #include "qemu/error-report.h"
 +#include "hw/virtio/virtio-bus.h"
  #ifdef CONFIG_XEN
  #  include <xen/hvm/hvm_info_table.h>
  #endif
 @@ -312,6 +313,10 @@ static void pc_init_pci(MachineState *machine)
static void pc_compat_2_3(MachineState *machine)
  {
 +    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
 +    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
 +
 +    k->queue_max = 64;
  }
static void pc_compat_2_2(MachineState *machine)
 diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
 index e67f2de..ff7c414 100644
 --- a/hw/i386/pc_q35.c
 +++ b/hw/i386/pc_q35.c
 @@ -45,6 +45,7 @@
  #include "hw/usb.h"
  #include "hw/cpu/icc_bus.h"
  #include "qemu/error-report.h"
 +#include "include/hw/virtio/virtio-bus.h"
/* ICH9 AHCI has 6 ports */
  #define MAX_SATA_PORTS     6
 @@ -291,6 +292,10 @@ static void pc_q35_init(MachineState *machine)
static void pc_compat_2_3(MachineState *machine)
  {
 +    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
 +    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
 +
 +    k->queue_max = 64;
  }
static void pc_compat_2_2(MachineState *machine)
 diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
 index 8e43aa2..ee8f6a3 100644
 --- a/hw/ppc/spapr.c
 +++ b/hw/ppc/spapr.c
 @@ -50,6 +50,7 @@
  #include "hw/pci/pci.h"
  #include "hw/scsi/scsi.h"
  #include "hw/virtio/virtio-scsi.h"
 +#include "hw/virtio/virtio-bus.h"
#include "exec/address-spaces.h"
  #include "hw/usb.h"
 @@ -1827,6 +1828,10 @@ static const TypeInfo spapr_machine_info = {
static void spapr_compat_2_3(Object *obj)
  {
 +    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
 +    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
 +
 +    k->queue_max = 64;
  }
static void spapr_compat_2_2(Object *obj)
 diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
 index 7d01500..c510cb7 100644
 --- a/hw/virtio/virtio-pci.c
 +++ b/hw/virtio/virtio-pci.c
 @@ -42,7 +42,11 @@
   * configuration space */
#define VIRTIO_PCI_CONFIG_SIZE(dev) VIRTIO_PCI_CONFIG_OFF(msix_enabled(dev)) -#define VIRTIO_PCI_QUEUE_MAX 64 +/* The number was chose to be greater than both the the number of max + * vcpus supported by host and the number of max tuntap queues support
 + * by host and also leave some spaces for future.
 + */
 +#define VIRTIO_PCI_QUEUE_MAX 1024
static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size,
                                 VirtIOPCIProxy *dev);
-- 2.1.0




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