Re: [Xen-devel] [PATCH 4/6] arm: add a small kconfig for Renesas RCar H3

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 24 Apr 2018, Julien Grall wrote:
> Hi,
> 
> On 04/24/2018 03:18 PM, Andrii Anisov wrote:
> > 
> > > Can you quantify what would be the cost of keeping that code around for
> > > IOMMU-less platform?
> > I'm not sure I understand your question. Do you mean a number of loc of the
> > passthrough feature for arm?
> 
> I meant that disabling something in Xen will come with a cost. While for a
> driver the maintenance is fairly minimal for anything touching core Xen it
> will require some more work for any change. So I understand that it will make
> Xen slightly smaller (~600 lines), but at what cost?
> 
> In other words, I am all for disabling unnecessary driver in Xen with some
> caveats (see my other answers). But I am quite worry on the burden for
> anything else without any real assessment.

It is very difficult to quantify the cost of adding a new Kconfig, I
don't think anybody would be able to answer that question :-)

But I think you have a point. When adding Kconfig options, it is easy to
forget the trade-offs and start adding one for everything. However, the
less self-contained the code, the higher the maintenance cost of the new
option.

PASSTHROUGH is an example of something very small in terms of lines of
code and not quite self-contained. A great example of something that
is probably not worth making optional.

My idea is to start from the low hanging fruits with high value returns
(lots of lines of code to remove). Once we are done with those, we can
go back and evaluate things like PASSTHROUGH.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel