On Thu, Nov 12, 2009 at 7:17 PM, Dean, David (I/S) <[email protected]> wrote:
> We have a z10 running zVM 5.4 in a dedicated LPAR with 3 dedicated IFL’s. > We have approximately 30 zLinux servers. Using IBM PerfKit, I list all of > the individual USER / zLinux CPU usages, each of which generally run in the > 1 to 5 % range. These servers do of course peak higher but on average they > are pretty low. We then take a look at the 3 IFL’s and see usage of maybe > 5% on each. Now, let’s say we have a USER / server or two or three go > berserk and peak CPU at 99 % for an extended period of time. We then look > at the IFL CPU usages and all three have climbed to maybe 10 to 15% each. Your numbers don't add up. If you have 30 Linux guests at 1-5% each, then you use 30-150% of an engine. With a 3-way z/VM you would have 10-50% utilization of each IFL - not 5% (sidebar: the cautious reader will notice a problem when the idle Linux guests use 5% each, you use half of your capacity just to keep the server warm - you need cheap agents to make this scale) If you would have 3 Linux guests with strong demand for CPU resources, you will indeed see all IFLs go to the max. If that max is very much below 100% then you're probably held back because you share the IFLs with other LPARs. There are some configuration mistakes to make. But you say you have dedicated IFLs for the LPAR, so we must rule that out. You can't have 3 Linux guests use 99% each and still have each of the 3 IFLs utilized for only 15%. That does not add up. So you're probably looking at the wrong things. What makes you determine these 3 Linux guests are not held back by something else? You're not looking at the Linux internal "vmstat" or "top" metrics, are you? And I hope you're not using the CP INDICATE command either (since that does a funny average). > How did the CPU get allocated? Is it always spread evenly across the IFL’s, > is that a setting? Why, if there were 3 USER / servers running at 99%, was > more CPU not allocated from the 3 IFL’s? Why did the IFL’s decide to > allocate X amount and go no further. You don't really allocate CPU. Basically, VM will give the available CPU resources to those who want it. When there is more demand than available resources, some users will have to wait before they get their share. The business may want to decide who should suffer less in that case, which is why we have SHARE settings and some other scheduler commands. > In the USER DIRECTORY I allocate storage but not CPU. As Marty mentions, you can set the SHARE value for the guests via commands or directory statements. A word of caution though: this stuff is not intuitive and you should not expect to get it right by reading the chapter of the book during your coffee break. You can do this work full time and still learn from new workloads. I have seen several customers fiddle with the settings based on intuition, casual reading, and bad examples. And they get it wrong. Always. You end up giving CPU resources to the wrong servers and buying more hardware to overcome wrong settings. Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/
