On Fri, May 1, 2009 at 1:12 AM, Leland Lucius <[email protected]> wrote:
> But, I'm curious why hottplugging CPUs doesn't do WAS any good? I was hoping you would ask ;-) The problem with idle Linux guests with multiple virtual CPUs is that Linux spreads the little work it has over all these virtual CPUs. So even when virtual CPUs properly drop from queue, CP will rarely find all virtual CPUs idle at the same time. This means that memory management on z/VM gets frustrated. But when cpuplugd "unplugs" additional virtual CPUs when the server is idle, CP has chance to take resources away. WAS (and JVM) have various things running that poll for work and thus never drop from queue. They can't be helped by by unplugging CPUs because the remaining one will be in-queue all day as well. The other effect from cpuplugd is that idle servers get prioritized over others to do the little work they have. That does not make sense to me. It's due to a design change in z/VM 5.4 (that I consider a design mistake) Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/ ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
