Re: [PATCH v7 09/18] virt: acrn: Introduce I/O request management

[Shuo A Liu]

On Mon 11.Jan'21 at 13:52:19 -0800, Davidlohr Bueso wrote:
> On Wed, 06 Jan 2021, shuo.a.liu@xxxxxxxxx wrote:
> > The processing flow of I/O requests are listed as following:
> >
> > a) The I/O handler of the hypervisor will fill an I/O request with
> >  PENDING state when a trapped I/O access happens in a User VM.
> > b) The hypervisor makes an upcall, which is a notification interrupt, to
> >  the Service VM.
> > c) The upcall handler schedules a tasklet to dispatch I/O requests.
> > d) The tasklet looks for the PENDING I/O requests, assigns them to
> >  different registered clients based on the address of the I/O accesses,
> >  updates their state to PROCESSING, and notifies the corresponding
> >  client to handle.
>
> Hmm so tasklets are deprecated (and have been for a while) and it's sad
> to see incoming new users in modern Linux. This wouldn't be the first one,
> however. We should be _removing_ users, not adding... In addition, this
> expands the whole tasklet_disable/enable() hacks.

Sorry, i had not noticed that.

> Could this not be done in process context instead?

It could be. The original consideration with tasklet was more about
performance as the I/O requests dispatching is a hot code path. I think
irq thread has little performance impact? I can have a try to convert
the tasklet to irq thread.

Thanks
shuo