On Mon, Oct 27, 2014 at 05:19:23PM +0800, Li Liu wrote: > > > On 2014/10/26 19:52, Michael S. Tsirkin wrote: > > On Sat, Oct 25, 2014 at 04:24:52PM +0800, john.liuli wrote: > >> From: Li Liu <john.liuli@xxxxxxxxxx> > >> > >> This set of patches try to implemet irqfd support of vhost-net > >> based on virtio-mmio. > >> > >> I had posted a mail to talking about the status of vhost-net > >> on kvm-arm refer to http://www.spinics.net/lists/kvm-arm/msg10804.html. > >> Some dependent patches are listed in the mail too. Basically the > >> vhost-net brings great performance improvements, almost 50%+. > >> > >> It's easy to implement irqfd support with PCI MSI-X. But till > >> now arm32 do not provide equivalent mechanism to let a device > >> allocate multiple interrupts. And even the aarch64 provid LPI > >> but also not available in a short time. > >> > >> As Gauguey Remy said "Vhost does not emulate a complete virtio > >> adapter but only manage virtqueue operations". Vhost module > >> don't update the ISR register, so if with only one irq then it's > >> no way to get the interrupt reason even we can inject the > >> irq correctly. > > > > Well guests don't read ISR in MSI-X mode so why does it help > > to set the ISR bit? > > Yeah, vhost don't need to set ISR under MSI-X mode. But for ARM > without MSI-X kind mechanism guest can't get the interrupt reason > through the only one irq hanlder (with one gsi resource). > > So I build a shared memory region to provide the interrupt reason > instead of ISR regiser by qemu without bothering vhost. Then even > there's only one irq with only one irq hanlder, it still can > distinguish why irq occur. > > Li. OK so this might allow sharing IRQs between config and VQs which might be a handy optimization even for PCI (at the moment reading ISR causes an exit). Need to see how all this would work on MP systems though. > > > > >> To get the interrupt reason to support such VIRTIO_NET_F_STATUS > >> features I add a new register offset VIRTIO_MMIO_ISRMEM which > >> will help to establish a shared memory region between qemu and > >> virtio-mmio device. Then the interrupt reason can be accessed by > >> guest driver through this region. At the same time, the virtio-mmio > >> dirver check this region to see irqfd is supported or not during > >> the irq handler registration, and different handler will be assigned. > >> > >> I want to know it's the right direction? Does it comply with the > >> virtio-mmio spec.? Or anyone have more good ideas to emulate mis-x > >> based on virtio-mmio? I hope to get feedback and guidance. > >> Thx for any help. > >> > >> Li Liu (2): > >> Add a new register offset let interrupt reason available > >> Assign a new irq handler while irqfd enabled > >> > >> drivers/virtio/virtio_mmio.c | 55 +++++++++++++++++++++++++++++++++++++++--- > >> include/linux/virtio_mmio.h | 3 +++ > >> 2 files changed, 55 insertions(+), 3 deletions(-) > >> > >> -- > >> 1.7.9.5 > >> > > > > . > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
