Re: [Qemu-ppc] [Qemu-devel] [PATCH V5 16/18] virtio-pci: increase the maximum number of virtqueues to 513

[Jason Wang]

On Wed, Apr 8, 2015 at 4:13 PM, Alexander Graf <address@hidden> wrote:
> >  Am 08.04.2015 um 10:10 schrieb Jason Wang <address@hidden>:
> >  
> >  
> >  
> > >  On 04/08/2015 12:54 AM, Alexander Graf wrote:
> > > >  On 04/01/2015 10:15 AM, 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.
> > > >  
> > > >  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.
> > > >  
> > > >  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 | 2 +-
> > > >   4 files changed, 16 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 9a5242a..02e3ce8 100644
> > > >  --- a/hw/virtio/virtio-pci.c
> > > >  +++ b/hw/virtio/virtio-pci.c
> > > >  @@ -42,7 +42,7 @@
> > > >    * configuration space */
> > > >   #define VIRTIO_PCI_CONFIG_SIZE(dev)    
> > > >  VIRTIO_PCI_CONFIG_OFF(msix_enabled(dev))
> > > >   -#define VIRTIO_PCI_QUEUE_MAX 64
> > > >  +#define VIRTIO_PCI_QUEUE_MAX 513
> > >  
> > >  513 is an interesting number. Any particular reason for it? Maybe 
> > > this
> > >  was mentioned before and I just missed it ;)
> > >  
> > >  
> > >  Alex
> >  
> >  The number were chose to match kernel limit for tuntap queues.  
> > Recent
> >  kernel allow up to 256 queues for tuntap, so 513 is in fact 256 * 2 
> > plus
> >  1 control vq.
>
> I see. I'm not fully convinced that it's a good idea to bake that 
> limit into qemu, but we have to have a limit somewhere.
>
> However, could you please make it more obvious in the code where thid 
> number stems from? Either by using defines or with a comment.
>
>
> Alex

Will add a comment for this.

Thanks.