Robert Love Explains Variable HZ

An anonymous reader writes "Robert Love, author of the kernel preemption patch for Linux, has backported a new performancing boosting patch from the 2.5 development kernel to the 2.4 stable kernel. This patch allows one to tune the frequency of the timer interrupt, defined in 2.4 as "HZ=100". Robert explains 'The timer interrupt is at the heart of the system. Everything lives and dies based on it. Its period is basically the granularity of the system: timers hit on 10ms intervals, timeslices come due at 10ms intervals, etc.' The 2.5 kernel has bumped the HZ value up to 1000, boosting performance."

Comments

Re:Moore's law

[WolfWithoutAClause]

Whoa! What architecture is that!

All of them AFAIK.

That just doesn't sound right.

Well, it is. Deal ;-)

The problem occurs when the memory management unit gets modified to maintain the virtual memory 'illusion'. Then you have to flush the caches to maintain consistency. Of course it doesn't happen on every clock tick, you hope.

That means that all the caches above the memory management unit need to get flushed. This includes the program cache; and any other data too.

I did a quick check on the web for this, but I haven't managed to find a good reference to where the MMU is placed in the different architectures yet.

Anyway, that's one of the main reasons the OS scheduling isn't shorter, but any decent OS has to do quite a bit of dorking around at that time.