Date: Wed, 20 Aug 2014 09:19:56 +0000 From: Wei Hu <weh@microsoft.com> To: "freebsd-drivers@freebsd.org" <freebsd-drivers@freebsd.org>, "freebsd-xen@freebsd.org" <freebsd-xen@freebsd.org> Cc: "freebsd-virtualization@freebsd.org" <freebsd-virtualization@freebsd.org> Subject: Directly reserve an interrupt IDT entry for Hyper-V Message-ID: <3defccd56bc0407c88bdda139b2462ac@BY1PR0301MB0902.namprd03.prod.outlook.com>
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Hello,
Sending to Xen, drivers and virtualization mailing lists since this might b=
e 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 h=
andle the host-guest channel communications on all vCPUs simultaneously. In=
order to achieve this, the hypervisor will send same interrupt concurrentl=
y on all the vCPUs. The traditional way on FreeBSD to set up interrupt hand=
ling for devicse, such as calling bus_alloc_resource() to reserve an IRQ li=
ne, and then calling bus_setup_intr() to create a vector, doesn't seem to w=
ork in this case. It seems if the interrupt is routed via legacy IRQ, it ca=
n only be active on one vCPU at a time. In order to allow the same interrup=
t 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:
#ifdef XENHVM
setidt(IDT_EVTCHN, &IDTVEC(xen_intr_upcall), SDT_SYSIGT, SEL_UPL, 0=
);
#else
setidt(IDT_EVTCHN, &IDTVEC(hv_vmbus_intr), SDT_SYSIGT, SEL_UPL, 0);
#endif
2. Apic_vector.S
Add IDTVEC(hv_vmbus_intr) to call Hyper-V vmbus interrupt service routine.
Any thoughts, objections and feedbacks are all welcome.
Thanks,
Wei Hu
Open Source Technology Center
Microsoft China
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