On 1/9/07, Ingo Adlung <[EMAIL PROTECTED]> wrote:
I would be surprised if it would not "run", however, from a performance pespective you would not want to overcommit the physically available CPUs for a single guest. I would not recommend to configure guests with a larger SMP than the underpinnng physical infrastructure provides backing for, i.e. if there is only one CPU available to VM the guests should also be uni- processor guests only. If you want/need to exploit SMP in guests based on workload requirements VM should also have at least as many processors available to itself and hence be able to dispatch to its guests as required.
Why is the number of physically available CPU's an relevant? (and I assume you mean logical CPU's defined to your LPAR, to start with). What's the odds of all our virtual CPU's being dispatched at the same time when the number of virtual CPU' s is the same as the number of logical CPU's defined for your LPAR. And what's the odds of those being dispatched all at the same time on real CPU's. Adding more virtual CPU's increases Linux overhead. So unless you need on average more than a full CPU, having another virtual CPU will at least increase the cost. And in most cases it will slow you down. Especially when lock contention happens in Linux and one virtual CPU spinning for the lock prevents the other one from getting resources to free the lock. Resource requirements of the application should be the key, not the installed resources for the entire machine. And I admit, that is harder to do if you don't measure resource usage. Rob PS A neat way to settle this argument in your shop with the Linux admin people is to give them extra virtual CPU's without adjusting the SHARE setting. It will make the virtual CPU's end up further down in the queue and with enough contention it will slow down your Linux application. -- Rob van der Heij Velocity Software, Inc http://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
