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Originally Posted by eric71
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 My info may be outdated, but the Ubuntu lowlatency kernels have the timer set for 1000 Hz, which is needed for good low latency work, especially midi.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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A little suplementary info for understanding what the timer is for:
Quote:
Timer Wheel, Jiffies and HZ (or, the way it was)
The original kernel timer system (called the "timer wheel) was based on incrementing a kernel-internal value (jiffies) every timer interrupt. The timer interrupt becomes the default scheduling quantum, and all other timers are based on jiffies. The timer interrupt rate (and jiffy increment rate) is defined by a compile-time constant called HZ. Different platforms use different values for HZ. Historically, the kernel used 100 as the value for HZ, yielding a jiffy interval of 10 ms. With 2.4, the HZ value for i386 was changed to 1000, yeilding a jiffy interval of 1 ms. Recently (2.6.13) the kernel changed HZ for i386 to 250. (1000 was deemed too high).
https://elinux.org/Kernel_Timer_Syst..._way_it_was.29
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If anyone has a link to better info (or first hand knowledge), please post it.
So it seems that the timer frequency is the interval for scheduling interrupts or context switching.