We just ipled a new VM4.3 cp load module to install VM63282. We currently have 7 Linux guests (SLES8 Kernel 2.4.19-3suse-SMP (ttyS0)) that are always in Q3. After VM63282, they are still in Q3. No change. I noticed that Bill mentioned a timer patch for the Linux guests. Is this included in the Service Pack 2 for the SuSE Linux Enterprise Server 8 for IBM Mainframes? Where can I direct our Linux sysadmins to get this patch, and will it allow the guests to go idle and drop out of Q3?
We are about to bring up 100+ Linux guests for student use, but are concerned about the Q3 problem and its implications. Should we be worried about the Linux guests staying in Q3?
TIA,
Scott
At 08:30 AM 8/20/2003, you wrote:
Marcy, As you probably know, this APAR was designed to allow idle Linux Guests to drop from the dispatch list when they go idle. Previously if a guest had an outstanding I/O, it would not be dropped from dispatch list. Which, ordinarily, would be a good thing to avoid overhead of dropping guest, only to re-dispatch shortly when the I/O completes. However, network I/O could often be seldom-ending channel programs or include never ending I/Os for initiation of QDIO devices. This APAR changes the definition of 'outstanding' I/O to avoid most of these cases.
The feedback we have seen so far and from internal tests show the following potential differences: 1. Guests are actually going dormant, leading to shorter dispatch lists. 2. Since Relative Share values are computed based on the total shares of users in the dispatch list, those normalized shares could be some what different. (i.e. If you used high relative share values, perhaps they don't need to be as high). 3. Storage management is more efficient. While 'dropping from dispatch list' is not required for trimming (we removed the true trim function in the early 1990s), it does allow for more intelligent stealing in removing dormant guest pages instead of active guest pages. 4. Guests may still be staying in the dispatch list for other reasons. The most common is for test idle condition, particularly if Linux guests are not running with the Timer Patch. 5. There will be a shift in the results shown on various User State Sampling reports from "I/O Active" to either "Dormant" or "Test Idle". 6. Potential for change in reported transaction rates. Drops from the dispatch list influence the schedulers 'Transaction' definition.
Bill Bitner - VM Performance Evaluation - IBM Endicott - 607-429-3286
************************************************************************** Scott Archer
Mainframe Systems Administration, New Mexico State University E-mail: [EMAIL PROTECTED] URL: http://sarcher.nmsu.edu Phone: (505)646-6186 **************************************************************************
