Occasionally I am forced to build larger parts of kernel, not only the “hot area”. This is mainly caused trough modified header files at a prominent position (e.g. tcp.h) or through some updates where the timestamps are updated. Depending on the current workload I restrict the CPU usage by not provide the full SMP load via -j N.

But this is one kind of load – the other is IO/disk load. So as I said sometimes I want restrict IO usage too. Via ionice it is possible to set the program IO scheduling class:

• Idle, get only get disk time when no other program has asked for disk IO
• Best effort (aka none class), standard IO class for a program. A feature of this class is that an IO priority can be assigned. Range from 0 (highest) to 7 (lowest). Within the same priority IO is scheduled in a round robin fashion. Without any modification the standard IO priority is derived from the CPU nice level: (cpu nice level + 20) / 5
• Real time, behaves similar to the realtime CPU class and can starve the IO subsystem. I have no use case and therefore never used it.

If I want to reduce the IO impact of the compile process I type the following command to set the IO scheduling class of the shell to idle. All derived processes (via fork()/exec()) will inherit the scheduling class.

ionice -c3 -p$$

PS: it works only with the completely fair queueing IO scheduler (cat /sys/block/*/queue/scheduler)