On Fri, Jan 8, 2010 at 1:56 PM, Agblad Tore <tore.agb...@volvo.com> wrote:
> SLES also have the hz_timer file. > It is zero here as well, SLES10 SP2, z10. > and the HZ contains 100. Correct. The "hz_timer" is to enable the "tick timer" - the "0" setting is the right one, since that gets us the "tickless timer" which avoids overhead. When the other platforms changed from 10 ms to 1 ms granularity, s390 did not dare because it would seriously impact installations that still run with the "tick timer" on. With the tickless timer, it would be helpful for granularity of the CPU metrics to have HZ raised to 1000. But.. The HZ also determines the granularity of wake-up requests. Some applications misbehave and ask to sleep for very short delays (polling). Today (after the right kernel fixes) these get rounded up to the next 10 ms. So even when some application is polling with 1 ms (!) delay, the process will wake up "only" once every 10 ms. Waking up the server every ms would be 10 times as much expensive. The 10 ms granularity also helps to improve timer merging, again reducing the overhead in a virtualized environment. Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/ ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
