On Wed, Jul 25, 2012 at 2:29 PM, Nadav Har'El <[email protected]>wrote:
> > HZ used to default to 100 in the Linux kernel, but now it actually > defaults (unless I'm mis-remembering) to 250, and this is where the 4-ms > resolution came from. Actually, there is the default HZ and inside the kernel HZ there is HZ that you can configure at compile time (with CONFIG_HZ) and USER_HZ, which, I think, is still 100 whether or not the kernel's HZ is customized. I think USER_HZ is what is important for "soft timers" you are interested in. Unless you configure the kernel yourself, the HZ value the kernel comes with probably depends on the distro. The tradeoff is as follows: desktop systems benefit from a higher HZ value because interactive processes are latency-sensitive. Servers, especially NUMA systems, don't have interactive processes and may, on the other hand, experience a lot of unpleasant effects (bus contention as an example) if there are lots of interrupts. Also note that the interrupt rate will be HZ*#CPUs. I am used to RedHat systems whose kernels normally come with HZ=100. You are talking about a server as well, right? You may be right about HZ=250 by default in the vanilla kernel that is supposed to be a compromise between 100 and 1000. If you go back to, say, 2.6.11 or 2.6.12, then you'll see HZ=1000 by default, I think. Was that "Linux on a desktop"? ;-) -- Oleg Goldshmidt | [email protected]
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