CPU discussion (RE: psutil.NUM_CPUS)
After my confusion on Paulo's patch a few weeks ago, I thought I had just gotten confused, and so I put psutil.NUM_CPUS in my SMT/HT patch. However, testing now on x86, I'm noticing a difference in the way Power and x86 report CPUS. On my laptop: <cpu> <arch>x86_64</arch> <model>SandyBridge</model> <vendor>Intel</vendor> <topology sockets='1' cores='2' threads='2'/> psutil.NUM_CPUS returns 4 On a Power7 system with 16 cores, 4 threads/core (so 64 total threads), psutil.NUM_CPUS returns 16. And this is, it turns out, because (and this sounds odd) for *guests* to be able to do SMT on Power, SMT has to be disabled. So, psutil.NUM_CPUS will not report the number of vCPUs that are available to guests. The same change would happen on x86 if you disabled HT, I assume. So, revisiting this difference that I noticed but wasn't able to articulate very well last time, do we want to make a change to the host code to use ppc64_cpu if the arch is Power, instead of psutil.NUM_CPUS? SMT *is* off, so, technically this isn't correct, but I think we should provide this information with guests in mind since we are a virtualization platform. Regards, - Christy
On 11/11/2014 07:31 PM, Christy Perez wrote:
After my confusion on Paulo's patch a few weeks ago, I thought I had just gotten confused, and so I put psutil.NUM_CPUS in my SMT/HT patch. However, testing now on x86, I'm noticing a difference in the way Power and x86 report CPUS.
On my laptop:
<cpu> <arch>x86_64</arch> <model>SandyBridge</model> <vendor>Intel</vendor> <topology sockets='1' cores='2' threads='2'/>
psutil.NUM_CPUS returns 4
On a Power7 system with 16 cores, 4 threads/core (so 64 total threads), psutil.NUM_CPUS returns 16.
And this is, it turns out, because (and this sounds odd) for *guests* to be able to do SMT on Power, SMT has to be disabled. So, psutil.NUM_CPUS will not report the number of vCPUs that are available to guests. The same change would happen on x86 if you disabled HT, I assume.
So, revisiting this difference that I noticed but wasn't able to articulate very well last time, do we want to make a change to the host code to use ppc64_cpu if the arch is Power, instead of psutil.NUM_CPUS? SMT *is* off, so, technically this isn't correct, but I think we should provide this information with guests in mind since we are a virtualization platform. why not use cpuinfo to determine the cpus? we are duplicating code today
Regards,
- Christy
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-- Ramon Nunes Medeiros Kimchi Developer Software Engineer - Linux Technology Center Brazil IBM Systems & Technology Group Phone : +55 19 2132 7878 ramonn@br.ibm.com
participants (2)
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Christy Perez -
Ramon Medeiros