On Mon, Jan 30, 2023 at 12:01:23PM +0200, Eli Cohen wrote: > On 30/01/2023 10:19, Jason Wang wrote: > > Hi Eli: > > > > On Mon, Jan 23, 2023 at 1:59 PM Eli Cohen <elic@xxxxxxxxxx> wrote: > > > VDPA allows hardware drivers the propagate interrupts from the hardware > > > directly to the vCPU used by the guest. In a typical implementation, the > > > hardware driver will assign the interrupt vectors to the virtqueues and report > > > this information back through the get_vq_irq() callback defined in > > > struct vdpa_config_ops. > > > > > > Interrupt vectors could be a scarce resource and may be limited. For such > > > cases, we can opt the administrator, through the vdpa tool, to set the policy > > > defining how to distribute the available vectors amongst the data virtqueues. > > > > > > The following policies are proposed: > > > > > > 1. First comes first served. Assign a vector to each data virtqueue by the > > > virtqueue index. Virtqueues which could not be assigned a dedicated vector > > > would use the hardware driver to propagate interrupts using the available > > > callback mechanism. > > > > > > vdpa dev add name vdpa0 mgmtdev pci/0000:86:00.2 int=all > > > > > > This is the default mode and works even if "int=all" was not specified. > > > > > > 2. Use round robin distribution so virtqueues could share vectors. > > > vdpa dev add name vdpa0 mgmtdev pci/0000:86:00.2 int=all intmode=share > > > > > > 3. Assign vectors to RX virtqueues only. > > > 3.1 Do not share vectors > > > vdpa dev add name vdpa0 mgmtdev pci/0000:86:00.2 int=rx > > > 3.2 Share vectors > > > vdpa dev add name vdpa0 mgmtdev pci/0000:86:00.2 int=rx intmode=share > > > > > > 4. Assign vectors to TX virtqueues only. Can share or not, like rx. > > > 5. Fail device creation if number of vectors cannot be fulfilled. > > > vdpa dev add name vdpa0 mgmtdev pci/0000:86:00.2 max_vq_pairs 8 int=rx intnum=8 > > I wonder: > > > > 1) how the administrator can know if there's sufficient resources for > > one of the above policies. > There's no established way to know. The idea is to use whatever there is > assuming interrupt bypassing is always better then the callback mechanism. > > 2) how does the administrator know which policy is the best assuming > > the resources are sufficient? (E.g vectors to RX only or vectors to TX > > only) > I don't think there's a rule of thumb here but he needs to experiment what > works best for him. > > > > If it requires a vendor specific way or knowledge, I believe it's > > better to code them in: > > > > 1) the vDPA parent or > > 2) underlayer management tool or drivers > > > > Thanks > > I was wondering also about the current mechanism we have. The hardware > driver reports irq number for each VQ. > > The guest driver sees a virtio pci device with MSIX vectors as the number of > virtqueues. > > Suppose the hardware driver provided only 5 interrupt vectors while there > are 16 VQs. > > Which MSIX vector at the guest gets really posted interrupt and which one > uses callback handled at the hardware driver? Not sure I understand. If you get a single interrupt from hardware callback or posted you can only drive one interrupt to guest, no? > > > > > > > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
