On Thu, Jul 16, 2020 at 09:39:17AM +0800, Zhu, Lingshan wrote: > > On 7/15/2020 9:43 PM, Jason Wang wrote: > > > On 2020/7/12 下午10:52, Zhu Lingshan wrote: > > Hi All, > > This series intends to implement IRQ offloading for > vhost_vdpa. > > By the feat of irq forwarding facilities like posted > interrupt on X86, irq bypass can help deliver > interrupts to vCPU directly. > > vDPA devices have dedicated hardware backends like VFIO > pass-throughed devices. So it would be possible to setup > irq offloading(irq bypass) for vDPA devices and gain > performance improvements. > > In my testing, with this feature, we can save 0.1ms > in a ping between two VFs on average. > > > > Hi Lingshan: > > During the virtio-networking meeting, Michael spots two possible issues: > > 1) do we need an new uAPI to stop the irq offloading? > 2) can interrupt lost during the eventfd ctx? > > For 1) I think we probably not, we can allocate an independent eventfd > which does not map to MSIX. So the consumer can't match the producer and we > fallback to eventfd based irq. > > Hi Jason, > > I wonder why we need to stop irq offloading, but if we need to do so, maybe a new uAPI would be more intuitive to me, > but why and who(user? qemu?) shall initialize this process, based on what kinda of basis to make the decision? > > For 2) it looks to me guest should deal with the irq synchronization when > mask or unmask MSIX vectors. > > Agreed! Well we need to make sure during a switch each interrupt is reported *somewhere*: either irq or eventfd - and not lost. > Thanks, > BR > Zhu Lingshan > > > What's your thought? > > Thanks > > > > > > Zhu Lingshan (7): > vhost: introduce vhost_call_ctx > kvm/vfio: detect assigned device via irqbypass manager > vhost_vdpa: implement IRQ offloading functions in vhost_vdpa > vDPA: implement IRQ offloading helpers in vDPA core > virtio_vdpa: init IRQ offloading function pointers to NULL. > ifcvf: replace irq_request/free with helpers in vDPA core. > irqbypass: do not start consumer or producer when failed to connect > > arch/x86/kvm/x86.c | 10 ++++-- > drivers/vdpa/ifcvf/ifcvf_main.c | 11 +++--- > drivers/vdpa/vdpa.c | 46 +++++++++++++++++++++++++ > drivers/vhost/Kconfig | 1 + > drivers/vhost/vdpa.c | 75 > +++++++++++++++++++++++++++++++++++++++-- > drivers/vhost/vhost.c | 22 ++++++++---- > drivers/vhost/vhost.h | 9 ++++- > drivers/virtio/virtio_vdpa.c | 2 ++ > include/linux/vdpa.h | 11 ++++++ > virt/kvm/vfio.c | 2 -- > virt/lib/irqbypass.c | 16 +++++---- > 11 files changed, 181 insertions(+), 24 deletions(-) > > > >
