> On May 2, 2019, at 9:43 AM, Ingo Molnar <mi...@kernel.org> wrote: > > > * Andy Lutomirski <l...@kernel.org> wrote: > >>> 8 gigabits/sec sounds good throughput in principle, if there's no >>> scalability pathologies with that. >> >> The latency is horrible. > > Latency would be amortized via batching anyway, so 8 gigabits/sec > suggests something on the order of magnitude of 4 bits per cycle, right? > With 64 bits extraction at a time that would be 16 cycles per 64-bit > word, which isn't too bad, is it?
I haven’t really dug in, but some Googling suggests that the 8Gbps figure is what you get with all cores doing RDRAND. It sounds like the actual RDRAND instruction doesn’t pipeline. > Making it "optional" is not really a technical argument in any way > though, either distros enable it in which case it's a de-facto default > setting, or they don't, in which case it de-facto almost doesn't exist. > > True.
