Hi folks,
I’m wondering if one of you could answer a couple of
questions with regards to the new Intel processors and VM scheduling when
hyperthreads are involved.
1) For
Nahelem/Westmere processors, Intel has a feature where it can turbo the processor’s
frequency. In an SMP environment, would this turbo boost affect Xen in
any ways? For example, does the TSC offset computation between processor’s
becomes invalid? Are there any other features or reasons why a Westmere
processor would cause a problem for Xen?
2) These new
processors have hyper threading enabled. Is Xen’s scheduling
algorithm cognizant of threads so that it can most effectively schedule VMs on idle
cores rather than use an idle thread on a busy core?
Let me explain that better.
For example, on 1 quad-core HT-enabled processor server, there are a
total of 8 working units (4 cores + 4 threads). Assume we labelt
them this way: [core#,thread#]: [0,0], [0,1], [1,0], [1,1], [2,0], [2,1],
[3,0], [3,1]. If there are 3 VMs exist, does the scheduler arrange the
VMs such that VM1 is on [0,0], VM2 is on [1,0], and VM3 on [2,0]? Or does
it tread all the work units without regards to their locations and schedule
them as [0,0], [0,1] and [1,0], for example? In the latter case, two VMs
are schedule on the same core, which would be less effective than scheduled on
the idle core.
Thanks
Roger
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