Re: [PATCH] pciehp: fast unplug for virtual machines

Michael S. Tsirkin
2021-11-12T10:09:38Z

On Fri, Nov 12, 2021 at 10:56:29AM +0100, Gerd Hoffmann wrote:
> Hi,
>
> > > This patch adds the fast_virtual_unplug module parameter to the
> > > pciehp driver. When enabled (which is the default) the linux
> > > kernel will simply skip the delay for virtual pcie ports, which
> > > reduces the total time for the unplug operation from 6-7 seconds
> > > to 1-2 seconds.
> >
> > BTW how come it's still taking seconds, not milliseconds?
>
> I've tackled the 5 seconds only, biggest chunk and easy target because
> the only reason to have that is to allow operators press the attention
> button again to cancel, so the risk to break something here is rather
> low.
>
> There are some more wait times elsewhere, to give the hardware the
> time needed when powering up/down slots, which sum up to roughly one
> second, and the time the driver needs to shutdown the device goes on
> top of that (typically not much).
>
> take care,
> Gerd

Probably also unnecessary for a virtual bridge. We'll need to fix these
up if we want native hotplug to be useful for workloads like kata -
these expect hotplug time in the milliseconds.

--
MST