Re: [PATCH 0/6] RfC: try improve native hotplug for pcie root ports

[Gerd Hoffmann]

On Mon, Oct 18, 2021 at 11:36:45AM -0400, Michael S. Tsirkin wrote:
> On Mon, Oct 11, 2021 at 02:04:58PM +0200, Gerd Hoffmann wrote:
> > 
> > 
> > Gerd Hoffmann (6):
> >   pci: implement power state
> >   pcie: implement slow power control for pcie root ports
> >   pcie: add power indicator blink check
> >   pcie: factor out pcie_cap_slot_unplug()
> >   pcie: fast unplug when slot power is off
> >   pcie: expire pending delete
> 
> So what's left to do here?
> I'm guessing more testing?

Yes.  Maybe ask rh qe to run the patch set through their hotplug test
suite (to avoid a apci-hotplug style disaster where qe found various
issues after release)?

> I would also like to see a shorter timeout, maybe 100ms, so
> that we are more responsive to guest changes in resending request.

I don't think it is a good idea to go for a shorter timeout given that
the 5 seconds are in the specs and we want avoid a resent request being
interpreted as cancel.

It also wouldn't change anything at least for linux guests because linux
is waiting those 5 seconds (with power indicator in blinking state).
Only the reason for refusing 'device_del' changes from "5 secs not over
yet" to "guest is busy processing the hotplug request".

We could consider to tackle the 5sec timeout on the guest side, i.e.
have linux skip the 5sec wait in case the root port is virtual (should
be easy to figure by checking the pci id).

take care,
  Gerd