Re: [PATCH v7 04/14] xen/arm: add Dom0 cache coloring support

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 27 Mar 2024, Julien Grall wrote:
> Hi,
> 
> On 27/03/2024 11:39, Carlo Nonato wrote:
> > On Fri, Mar 22, 2024 at 8:26 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
> > > 
> > > On 21.03.2024 18:31, Carlo Nonato wrote:
> > > > On Thu, Mar 21, 2024 at 4:57 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
> > > > > 
> > > > > On 21.03.2024 16:04, Carlo Nonato wrote:
> > > > > > On Tue, Mar 19, 2024 at 4:30 PM Jan Beulich <jbeulich@xxxxxxxx>
> > > > > > wrote:
> > > > > > > On 15.03.2024 11:58, Carlo Nonato wrote:
> > > > > > > > --- a/docs/misc/xen-command-line.pandoc
> > > > > > > > +++ b/docs/misc/xen-command-line.pandoc
> > > > > > > > @@ -963,6 +963,15 @@ Controls for the dom0 IOMMU setup.
> > > > > > > > 
> > > > > > > >   Specify a list of IO ports to be excluded from dom0 access.
> > > > > > > > 
> > > > > > > > +### dom0-llc-colors
> > > > > > > > +> `= List of [ <integer> | <integer>-<integer> ]`
> > > > > > > > +
> > > > > > > > +> Default: `All available LLC colors`
> > > > > > > > +
> > > > > > > > +Specify dom0 LLC color configuration. This option is available
> > > > > > > > only when
> > > > > > > > +`CONFIG_LLC_COLORING` is enabled. If the parameter is not set,
> > > > > > > > all available
> > > > > > > > +colors are used.
> > > > > > > 
> > > > > > > My reservation towards this being a top-level option remains.
> > > > > > 
> > > > > > How can I turn this into a lower-level option? Moving it into
> > > > > > "dom0=" doesn't
> > > > > > seem possible to me. How can I express a list (llc-colors) inside
> > > > > > another list
> > > > > > (dom0)? dom0=llc-colors=0-3,12-15,other-param=... How can I stop
> > > > > > parsing
> > > > > > before reaching other-param?
> > > > > 
> > > > > For example by using a different separator:
> > > > > 
> > > > > dom0=llc-colors=0-3+12-15,other-param=...
> > > > 
> > > > Ok, but that would mean to change the implementation of the parsing
> > > > function
> > > > and to adopt this syntax also in other places, something that I would've
> > > > preferred to avoid. Anyway I'll follow your suggestion.
> > > 
> > > Well, this is all used by Arm only for now. You will want to make sure Arm
> > > folks are actually okay with this alternative approach.
> > > 
> > > Jan
> > 
> > Are you Arm maintainers ok with this?
> 
> Unfortunately no. I find the use of + and "nested" = extremely confusing to
> read.
> 
> There might be other symbols to use (e.g. s/=/:/ s#+#/#), but I am not
> entirely sure the value of trying to cram all the options under a single
> top-level parameter. So I right now, I would prefrr if we stick with the
> existing approach (i.e. introducing dom0-llc-colors).

I also prefer the original as suggested in this version of the patch