On Thu, 23 Sep 2010, Christian Riesch wrote: > > > It implies clock tuning in userspace for a potential sub microsecond > > > accurate clock. The clock accuracy will be limited by user space > > > latencies and noise. You wont be able to discipline the system clock > > > accurately. > > > > Noise matters, latency doesn't. > > Well put! That's why we need hardware support for PTP timestamping to reduce > the noise, but get along well with the clock servo that is steering the PHC in > user space. Even if I buy into the catch phrase above: User space is subject to noise that the in kernel code is not. If you do the tuning over long intervals then it hopefully averages out but it still causes jitter effects that affects the degree of accuracy (or sync) that you can reach. And the noise varies with the load on the system. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
