G'day all, Just went through the process of building a new 2.4.19 kernel with timer patch applied (linux-2.4.19-timer-1-may2002 from DevWorks). I wonder if anyone has seen the /proc/sys/kernel/hz_timer pseudofile, and can describe its function.
Full story, read on... When building the kernel, I noticed a new option: [*] No HZ timer ticks in idle [ ] Idle HZ timer on by default <-- new one I read this as "do you want to enable the no-HZ function in your kernel, but turn it off by default at IPL-time". Based on this, I left it as shown above for my kernel build (because I wanted the patched function, not the old function). After I IPLed, IND Q EXP told me that my idle guest was still constantly sitting in Q3. Then I thought about the new kernel option, and theorised that if there's an option that allows you to set the default operation at IPL time there's likely to be a way to change it while running... A brief search yielded /proc/sys/kernel/hz_timer, which was set to 1. I echoed 0, and the system still worked, but still seemed to be constantly active in Q3. Looking at the patch file it would appear that it shoud be 0 to enable the 'no-HZ' function, but it's not clear (to me, at least). I must confess that for all of my advocacy of the timer patch, this is the first time I've used it on a system under VM. So I admit that I'm not sure what I should be seeing from VM's perspective. Does /proc/sys/kernel/hz_timer do what I think it does? Am I confusing myself looking at IND Q? Will our (to-be-installed-RSN) z/VM monitoring tool tell me the real story? Thanks in advance, Vic Cross
