Linux Kernel Development (Developer's Library) by Robert Love

Author:Robert Love [Robert Love]
Language: eng
Format: epub
Publisher: Pearson Education
Published: 2010-06-21T22:00:00+00:00

Disadvantages with a Larger HZ

Now, there must be some downside to increasing the tick rate, or it would have been 1000Hz (or even higher) to start. Indeed, there is one large issue: A higher tick rate implies more frequent timer interrupts, which implies higher overhead, because the processor must spend more time executing the timer interrupt handler. The higher the tick rate, the more time the processor spends executing the timer interrupt. This adds up to not just less processor time available for other work, but also a more frequent thrashing of the processor’s cache and increase in power consumption. The issue of the overhead’s impact is debatable. A move from HZ=100 to HZ=1000 clearly brings with it ten times greater overhead. However, how substantial is the overhead to begin with? The final agreement is that, at least on modern systems, HZ=1000 does not create unacceptable overhead and the move to a 1000Hz timer has not hurt performance too much. Nevertheless, it is possible in 2.6 to compile the kernel with a different value for HZ . 3

3 Because of architectural and NTP-related issues, however, not just any value is acceptable for HZ . On x86, 100, 500, and 1000 all work fine.

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