On Tue, 2013-10-01 at 11:39 +0300, Gleb Natapov wrote: > On Tue, Oct 01, 2013 at 06:34:26PM +1000, Michael Ellerman wrote: > > On Thu, Sep 26, 2013 at 11:06:59AM +0200, Paolo Bonzini wrote: > > > Il 26/09/2013 08:31, Michael Ellerman ha scritto: > > > > Some powernv systems include a hwrng. Guests can access it via the > > > > H_RANDOM hcall. > > > > > > Is there any reason to do this in the kernel? > > > > It's less code, and it's faster :) > > > > > It does not have to be a particularly fast path; > > > > Sure, but do we have to make it slow on purpose? > > > We do not put non performance critical devices into the kernel. So for the sake of that dogma you are going to make us do something that is about 100 times slower ? (and possibly involves more lines of code) It's not just speed ... H_RANDOM is going to be called by the guest kernel. A round trip to qemu is going to introduce a kernel jitter (complete stop of operations of the kernel on that virtual processor) of a full exit + round trip to qemu + back to the kernel to get to some source of random number ... this is going to be in the dozens of ns at least. This makes no sense. Ben. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
