[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] tools/libxc: Avoid hypercalls for cacheflush on x86
On 04/03/14 01:14, Ian Campbell wrote: > 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. > For booting a single guest, noone will notice. Booting 10 or more at a time however is very different. XenServer, along with all other virtualisation platforms live in a world where "Net time to boot $N guests" (where N is measured in hundreds) is an important quantity, and needless overhead from things like this cause dom0 needless load that it would rather do without. I should say that I have not done any performance metrics on this - as noted in the patch I stumbled upon it with valgrind. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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