Re: [Qemu-devel] [PATCH V7 15/16] virtio-pci: increase the maximum number of virtqueues to 513

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

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.

> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Alexander Graf <agraf@suse.de>
> Cc: qemu-ppc@nongnu.org
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  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