Re: [PATCH] Replace kvm io delay pv-ops with linux magic

[Alok Kataria <akataria@vmware.com>]

On Thu, 2009-11-19 at 18:08 -0800, Jeremy Fitzhardinge wrote:
> On 11/20/09 09:59, Alexander Graf wrote:
> >
> > On 20.11.2009, at 02:54, Jeremy Fitzhardinge wrote:
> >
> >> On 11/20/09 07:58, Alexander Graf wrote:
> >>>
> >>> Am 19.11.2009 um 23:55 schrieb Jeremy Fitzhardinge <jeremy@goop.org>:
> >>>
> >>>> On 11/18/09 20:56, Alexander Graf wrote:
> >>>>> Currently we use pv-ops to tell linux not to do anything on io_delay.
> >>>>>
> >>>>> While the basic idea is good IMHO, I don't see why we would need
> >>>>> pv-ops
> >>>>> for that. The io delay function already has a switch that can do
> >>>>> nothing
> >>>>> if you're so inclined.
> >>>>>
> >>>>> So here's a patch (stacked on top of the previous pv-ops series) that
> >>>>> removes the io delay pv-ops hook and just sets the native io delay
> >>>>> variable instead.
> >>>>>
> >>>>
> >>>> Can you just get rid of the io_delay op altogether?  If KVM doesn't
> >>>> need
> >>>> it, then nobody does.
> >>>
> >>> Sure, can do. That'd be a separate patch though.
> >>
> >> Yep.  A patch each for VMI and Xen to remove the dependency, and a final
> >> patch to remove the op.  Hm, looks like VMI has a specific ROM call for
> >> io_delay; I wonder what it does.
> >
> > Oh so it's actually using it? Feel like doing the removal then? I
> > don't really want to mess with VMI code :-)
> 
> I would post the patch and see if Alok naks it.  But I somehow doubt
> vmware is doing anything profound with that call.
> 

Yeah removing it is fine with me. That call is just a no-op anyways,
and, if there are other ways for avoiding the IO delay cost we can use
that one too.

Alok