linux-kernel - Re: [PATCH] pciehp: fast unplug for virtual machines

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Message-ID: <20211112095629.uoxfuhsvhicsdxgd@sirius.home.kraxel.org>
Date:   Fri, 12 Nov 2021 10:56:29 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pciehp: fast unplug for virtual machines

  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