On Fri, Jul 21, 2017 at 04:55:12PM +0200, Oliver Mangold wrote: > On 21.07.2017 16:47, Theodore Ts'o wrote: > > On Fri, Jul 21, 2017 at 01:39:13PM +0200, Oliver Mangold wrote: > > > Better, but obviously there is still much room for improvement by reducing > > > the number of calls to RDRAND. > > Hmm, is there some way we can easily tell we are running on Ryzen? Or > > do we believe this is going to be true for all AMD devices? > I would like to note that my first measurement on Broadwell suggest that the > current frequency of RDRAND calls seems to slow things down on Intel also > (but not as much as on Ryzen). On my T470 laptop (with an Intel mobile core i7 processor), using your benchmark, I am getting 136 MB/s, versus your 75 MB/s. But so what? More realistically, if we are generating 256 bit keys (so we're reading from /dev/urandom 32 bytes at a time), it takes 2.24 microseconds per key generation. What do you get when you run: dd if=/dev/urandom of=/dev/zero bs=256 count=1000000 Even if on Ryzen it's slower by a factor of two, 5 microseconds per key generation is pretty fast! The time to do the Diffie-Hellman exchange and the RSA operations will probably completely swamp the time to generate the session key. And if you think 2.24 or 5 microseconds is to slow for the IV generation --- then use a userspace ChaCha20 CRNG for that purpose. I'm not really sure I see a real-life operational problem here. - Ted
