Re: [Xen-devel] [RFC PATCH] Adding support for coverage informations

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-01-30 at 21:34 +0000, Konrad Rzeszutek Wilk wrote:
> > The reason why adding a new hypercall instead of a new sysctl is simply
> > because is easier to have a zero cost if you disable coverage
> > informations. The best thing would be redirect do_coverage_op to
> > do_ni_hypercall using linker options but even two small stub would do
> > (these stubs will return ENOSYS instead).
> 
> I am not sure I follow. Is the sysctl hypercall code path "longer" than
> the hypercall path you are introducing? What is the zero cost?

I don't think we care a jot about the performance of this system call
when coverage is disabled, it's certainly not a hot path and in any case
if it is a NOP it doesn't really matter anyway.

Ian.


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