On Wed, Jan 5, 2022 at 4:37 PM Longpeng (Mike, Cloud Infrastructure Service Product Dept.) <longpe...@huawei.com> wrote: > > > > > -----Original Message----- > > From: Jason Wang [mailto:jasow...@redhat.com] > > Sent: Wednesday, January 5, 2022 3:54 PM > > To: Michael S. Tsirkin <m...@redhat.com> > > Cc: Longpeng (Mike, Cloud Infrastructure Service Product Dept.) > > <longpe...@huawei.com>; Stefan Hajnoczi <stefa...@redhat.com>; Stefano > > Garzarella <sgarz...@redhat.com>; Cornelia Huck <coh...@redhat.com>; > > pbonzini > > <pbonz...@redhat.com>; Gonglei (Arei) <arei.gong...@huawei.com>; Yechuan > > <yech...@huawei.com>; Huangzhichao <huangzhic...@huawei.com>; qemu-devel > > <qemu-devel@nongnu.org> > > Subject: Re: [RFC 02/10] vhost: add 3 commands for vhost-vdpa > > > > On Wed, Jan 5, 2022 at 3:02 PM Michael S. Tsirkin <m...@redhat.com> wrote: > > > > > > On Wed, Jan 05, 2022 at 12:35:53PM +0800, Jason Wang wrote: > > > > On Wed, Jan 5, 2022 at 8:59 AM Longpeng(Mike) <longpe...@huawei.com> > > > > wrote: > > > > > > > > > > From: Longpeng <longpe...@huawei.com> > > > > > > > > > > To support generic vdpa deivce, we need add the following ioctls: > > > > > - GET_VECTORS_NUM: the count of vectors that supported > > > > > > > > Does this mean MSI vectors? If yes, it looks like a layer violation: > > > > vhost is transport independent. > > > > > > Well *guest* needs to know how many vectors device supports. > > > I don't think there's a way around that. Do you? > > > > We have VHOST_SET_VRING/CONFIG_CALL which is per vq. I think we can > > simply assume #vqs + 1? > > > > > Otherwise guests will at best be suboptimal. > > > > > > > And it reveals device implementation > > > > details which block (cross vendor) migration. > > > > > > > > Thanks > > > > > > Not necessarily, userspace can hide this from guest if it > > > wants to, just validate. > > > > If we can hide it at vhost/uAPI level, it would be even better? > > > > Not only MSI vectors, but also queue-size, #vqs, etc.
MSI is PCI specific, we have non PCI vDPA parent e.g VDUSE/simulator/mlx5 And it's something that is not guaranteed to be not changed. E.g some drivers may choose to allocate MSI during set_status() which can fail for various reasons. > > Maybe the vhost level could expose the hardware's real capabilities > and let the userspace (QEMU) do the hiding? The userspace know how > to process them. #MSI vectors is much more easier to be mediated than queue-size and #vqs. For interrupts, we've already had VHOST_SET_X_KICK, we can keep allocating eventfd based on #MSI vectors to make it work with any number of MSI vectors that the virtual device had. For queue-size, it's Ok to have a new uAPI but it's not a must, Qemu can simply fail if SET_VRING_NUM fail. For #vqs, it's OK to have a new uAPI since the emulated virtio-pci device requires knowledge the #vqs in the config space. (still not a must, we can enumerate #vqs per device type) For the config size, it's OK but not a must, technically we can simply relay what guest write to vhost-vdpa. It's just because current Qemu require to have it during virtio device initialization. Thanks > > > Thanks > > > > > > > > > > > > > - GET_CONFIG_SIZE: the size of the virtio config space > > > > > - GET_VQS_NUM: the count of virtqueues that exported > > > > > > > > > > Signed-off-by: Longpeng <longpe...@huawei.com> > > > > > --- > > > > > linux-headers/linux/vhost.h | 10 ++++++++++ > > > > > 1 file changed, 10 insertions(+) > > > > > > > > > > diff --git a/linux-headers/linux/vhost.h b/linux-headers/linux/vhost.h > > > > > index c998860d7b..c5edd75d15 100644 > > > > > --- a/linux-headers/linux/vhost.h > > > > > +++ b/linux-headers/linux/vhost.h > > > > > @@ -150,4 +150,14 @@ > > > > > /* Get the valid iova range */ > > > > > #define VHOST_VDPA_GET_IOVA_RANGE _IOR(VHOST_VIRTIO, 0x78, \ > > > > > struct > > > > > vhost_vdpa_iova_range) > > > > > + > > > > > +/* Get the number of vectors */ > > > > > +#define VHOST_VDPA_GET_VECTORS_NUM _IOR(VHOST_VIRTIO, 0x79, int) > > > > > + > > > > > +/* Get the virtio config size */ > > > > > +#define VHOST_VDPA_GET_CONFIG_SIZE _IOR(VHOST_VIRTIO, 0x80, int) > > > > > + > > > > > +/* Get the number of virtqueues */ > > > > > +#define VHOST_VDPA_GET_VQS_NUM _IOR(VHOST_VIRTIO, 0x81, int) > > > > > + > > > > > #endif > > > > > -- > > > > > 2.23.0 > > > > > > > > >
