Re: [Xen-devel] [PATCH] tools/libxc: Avoid hypercalls for cacheflush on x86

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2014-03-03 at 16:22 +0000, Ian Jackson wrote:
> Andrew Cooper writes ("[PATCH] tools/libxc: Avoid hypercalls for cacheflush 
> on x86"):
> > XEN_DOMCTL_cacheflush hypercalls are -ENOSYS on x86.  As domain
> > creation/migration is already very hypercall-heavy, avoid making extra
> > redundant hypercalls
> 
> Surely this should be done by moving the relevant code to an
> arm-specific file, not by #ifdeffery.

I think it is very debatable that sort-circuiting a single ENOSYS
hypercall in the tools is even worth it at all. "very hypercall heavy"
doesn't cut it as a rationale IMHO. Unless an actual demonstrable
improvement is seen, perhaps over a larger series removing a large
number of so called redundant calls, it's just an additional source of
confusion (due to gating at multiple levels) as far as I'm concerned.

Ian.


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