Messages in this thread | | | Date | Wed, 25 Apr 2001 22:30:30 -0400 (EDT) | From | Werner Puschitz <> | Subject | Re: #define HZ 1024 -- negative effects? |
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On Wed, 25 Apr 2001, Dan Maas wrote:
> > Are there any negative effects of editing include/asm/param.h to change > > HZ from 100 to 1024? Or any other number? This has been suggested as a > > way to improve the responsiveness of the GUI on a Linux system. > > I have also played around with HZ=1024 and wondered how it affects > interactivity. I don't quite understand why it could help - one thing I've > learned looking at kernel traces (LTT) is that interactive processes very, > very rarely eat up their whole timeslice (even hogs like X). So more > frequent timer interrupts shouldn't have much of an effect... > > If you are burning CPU doing stuff like long compiles, then the increased HZ > might make the system appear more responsive because the CPU hog gets > pre-empted more often. However, you could get the same result just by > running the task 'nice'ly...
A tradeoff of having better system responsiveness by having the kernel to check more often if a running process should be preempted is that the CPU spends more time in Kernel Mode and less time in User Mode. And as a consequence, user programs run slower.
Regards, Werner
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