Re: [Xen-devel] [PATCH 6/7] x86/viridian: make the threshold for HvNotifyLongSpinWait tunable

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Andrew Cooper
> Sent: 20 March 2017 17:03
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Subject: Re: [PATCH 6/7] x86/viridian: make the threshold for
> HvNotifyLongSpinWait tunable
> 
> On 17/03/17 09:57, Paul Durrant wrote:
> > The current threshold before the guest issues the hypercall is, and always
> > has been, hard-coded to 2047. It is not clear where this number came
> > from so, to at least allow for ease of experimentation, this patch makes
> > the threshold tunable via the Xen command line.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> 
> This is one example of a configuration option which I'd prefer to see
> done with the (planned) new CPUID interface.
> 
> The value here doesn't have any impact on the hypervisor, so a
> configuration option is free to be chosen entirely by the toolstack, and
> would also become inherently per-domain configuration rather than global.
> 
> Can I talk you into deferring this change until the CPUID interface is
> sorted, to avoid introducing yet another command line option?
> 

I don't really want to wait for something with no definite timescale. I don't 
see any harm in adding this and then stating it can be overridden by per-domain 
CPU policy later on. Presumably there's a bunch of other stuff where this would 
be the case.

  Paul

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel