Messages in this thread | | | From | Yongji Xie <> | Date | Tue, 28 Mar 2023 11:03:11 +0800 | Subject | Re: [PATCH v4 03/11] virtio-vdpa: Support interrupt affinity spreading mechanism |
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On Fri, Mar 24, 2023 at 2:28 PM Jason Wang <jasowang@redhat.com> wrote: > > On Thu, Mar 23, 2023 at 1:31 PM Xie Yongji <xieyongji@bytedance.com> wrote: > > > > To support interrupt affinity spreading mechanism, > > this makes use of group_cpus_evenly() to create > > an irq callback affinity mask for each virtqueue > > of vdpa device. Then we will unify set_vq_affinity > > callback to pass the affinity to the vdpa device driver. > > > > Signed-off-by: Xie Yongji <xieyongji@bytedance.com> > > Thinking hard of all the logics, I think I've found something interesting. > > Commit ad71473d9c437 ("virtio_blk: use virtio IRQ affinity") tries to > pass irq_affinity to transport specific find_vqs(). This seems a > layer violation since driver has no knowledge of > > 1) whether or not the callback is based on an IRQ > 2) whether or not the device is a PCI or not (the details are hided by > the transport driver) > 3) how many vectors could be used by a device > > This means the driver can't actually pass a real affinity masks so the > commit passes a zero irq affinity structure as a hint in fact, so the > PCI layer can build a default affinity based that groups cpus evenly > based on the number of MSI-X vectors (the core logic is the > group_cpus_evenly). I think we should fix this by replacing the > irq_affinity structure with > > 1) a boolean like auto_cb_spreading > > or > > 2) queue to cpu mapping >
But only the driver knows which queues are used in the control path which don't need the automatic irq affinity assignment. So I think the irq_affinity structure can only be created by device drivers and passed to the virtio-pci/virtio-vdpa driver.
> So each transport can do its own logic based on that. Then virtio-vDPA > can pass that policy to VDUSE where we only need a group_cpus_evenly() > and avoid duplicating irq_create_affinity_masks()? >
I don't get why we would have duplicated irq_create_affinity_masks().
Thanks, Yongji
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