Sending to Xen, drivers and virtualization mailing lists since this might be of
interest to the folks on these aliases.
I am working for Microsoft to improve the performance of FreeBSD running on
Hyper-V. Right now I am adding a feature in the vmbus driver which could handle
the host-guest channel communications on all vCPUs simultaneously. In order to
achieve this, the hypervisor will send same interrupt concurrently on all the
vCPUs. The traditional way on FreeBSD to set up interrupt handling for devicse,
such as calling bus_alloc_resource() to reserve an IRQ line, and then calling
bus_setup_intr() to create a vector, doesn't seem to work in this case. It
seems if the interrupt is routed via legacy IRQ, it can only be active on one
vCPU at a time. In order to allow the same interrupt to be handled on all vCPUs
concurrently, all I need is an IDT entry, not an IRQ line.
I checked current FreeBSD code. It looks to me Xen directly uses the vector
number IDT_EVTCHN (0x93) to achieve the same purpose. I am proposing both Xen
and Hyper-V share this same vector. Following is a little bit detail of my
proposal for the changes in the current kernel.
1. In machdep.c:
setidt(IDT_EVTCHN, &IDTVEC(xen_intr_upcall), SDT_SYSIGT, SEL_UPL, 0);
setidt(IDT_EVTCHN, &IDTVEC(hv_vmbus_intr), SDT_SYSIGT, SEL_UPL, 0);
Add IDTVEC(hv_vmbus_intr) to call Hyper-V vmbus interrupt service routine.
Any thoughts, objections and feedbacks are all welcome.
Open Source Technology Center
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