Another thing to look at is how the kernel's timer is set. Some of the basic RT-kernels that distros have were not specifically intended for pro audio. My info may be outdated, but the Ubuntu lowlatency kernels have the timer set for 1000 Hz, which is needed for good low latency work, especially midi. That's one reason they were added, as the Ubuntustudio project was gaining traction. But I've see RT-kernels that use 100 Hz, and although they are full realtime preempt, the timer may be too slow for midi. In short, it's good to dig a little deeper into the kernel configuration. That's one reason the AVLinux RT kernels are good - they have been specifically configured for audio, and have the timer set accordingly.
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