Messages in this thread | | | Date | Sat, 21 Mar 2009 12:57:28 +0100 | From | Michal Simek <> | Subject | Re: [PATCH 08/57] microblaze_v7: Interrupt handling, timer support, selfmod code |
| |
Thomas Gleixner wrote: > On Sat, 21 Mar 2009, Michal Simek wrote: >> CONFIG_HZ_100=y >> # CONFIG_HZ_250 is not set >> # CONFIG_HZ_300 is not set >> # CONFIG_HZ_1000 is not set >> CONFIG_HZ=100 >> >> For NO_HZ val I shouldn't use HZ value because of NO_HZ and HZ values shouldn't >> be in .config file. Am I right? > > No. NO_HZ does not remove the HZ value from the kernel. There is way > too much code depending on it. What NO_HZ does is to supress the > periodic tick when the system goes idle and the next timer expiry is > farther away than 1 HZ. When the system is non idle then the periodic > tick runs again. NO_HZ is merily for power saving. > > In a normal kernel when the machine is idle then we wake up every HZ > to find out that there is no work to do and we go idle again. But if > you think about it then this is stupid, because the kernel knows when > the next timer is due to expire. So if the next timer expiry is > e.g. 100ms away, then we can sleep for full 100ms instead of sleeping > 10 * 10ms (HZ=100) or 100 * 1ms (HZ=1000). This allows systems to go > into deeper power saving states. > > You should be able to observe the difference by monitoring > /proc/interrupts. A nohz enabled kernel should have significantly less > timer interrupts on an idle system.
Yes, I see it. I think I sent my log in any previous email in this thread too + I see it on my heartbeat led too.
Thanks for explanation, Michal > > Thanks, > > tglx
-- Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854
| |