I have two machines running the 2.4.19 SLES 8 kernel. When I put "0" into hz_timer, I can see the utilization drop off the radar. When set to "1", it is at the usual .3% (on a MP3000, G5).
According to ESAMON, the machines sit in Q3 58% of the time. On Thursday 06 March 2003 08:34 pm, you wrote: > 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 -- Rich Smrcina Sr. Systems Engineer Sytek Services, A Division of DSG Milwaukee, WI [EMAIL PROTECTED] [EMAIL PROTECTED] Catch the WAVV! Stay for Requirements and the Free for All! Update your S/390 skills in 4 days for a very reasonable price. WAVV 2003 in Winston-Salem, NC. April 25-29, 2003 For details see http://www.wavv.org
