On 2026-03-19 03:43:12 [+0000], Michael Kelley wrote: > Indeed, yes, that would remove the need for all the per-CPU interrupt hackery > on x86/x64. I don't have any objection to someone pursuing that path, but it's > not something I can do. Full disclosure: You'll see my name on Hyper-V and > VMBus stuff in the Linux kernel, with Microsoft as my employer. But I retired > from Microsoft 2.5 years ago, and my current involvement in Linux kernel work > is purely as a very part-time volunteer. I also lack access to hardware and > the > test machinery needed to make more significant changes, particularly if > multiple > versions of Hyper-V must be tested.
right. Then I would only ask for better annotation instead this current thingy. > > I would be worried if the host would storming interrupts to the guest > > because it makes no progress. > > No, that kind of storming won't happen. The Hyper-V host<->guest > interface is based on message queues. The host interrupts the guest > if it puts a message in the queue that transitions the queue from > "empty" to "not empty". Eventually the tasklet enabled in vmbus_isr() > and its subsidiaries gets around to emptying the queue, which effectively > re-arms the interrupt. The host may add more messages to the queue, > but it doesn't interrupt again for that queue until the queue is empty. > If the guest is delayed in doing that emptying, nothing bad happens. Okay. > > > > Moving on. This (trying very hard here) even schedules tasklets. Why? > > > > You need to disable BH before doing so. Otherwise it ends in ksoftirqd. > > > > You don't want that. > > > > > > Again, Jan can comment on the impact of delays due to ending up > > > in ksoftirqd. > > > > My point is that having this with threaded interrupt support would > > eliminate the usage of tasklets. > > Agreed, probably. For the non-RT case, the latency in getting to the > tasklet code *does* matter. I'm not familiar with how tasklets compare > to threaded interrupts on latency. There shouldn't be much difference on level where it actually matters. Sebastian
