mortengh
Enthusiast
Enthusiast

Only about 50% CPU cycles available?

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Hello!

Hardware: SuperMicro A1SRM-2758F (8x2.4Ghz CPU - no hyper-threading), 32GB RAM

Hypervisor: ESXi-5.5 build 2068190

I have tried to create max CPU load on the system ("cat /dev/urandom >/dev/null" - started 10 times in parallel both on in the VM and on the ESXi host it self).

According to the hardware specs I should have 8x2.4Ghz = 19.2Ghz available.

I have:

   Configuration --> Hardware --> Power Managements --> Active Policy: High Performance

   Configuration --> Software --> System Resource Allocation --> System Resource Reservation --> CPU: 240 Mhz   (19.20Ghz - 0.24Ghz = 18.96Ghz for VMs)

So! Why is it that only 16.2Ghz is available for VMs (in 'Resource Allocation --> CPU --> Total Capacity)

And on the 'Summary' page CPU usage maxes out at 11.2Ghz?

Why can I only load my CPUs at about half the capacity?

Best regards,

- Morten Green Hermansen, Fanitas

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mortengh
Enthusiast
Enthusiast

Hello people!

Pressing 'p' in esxtop made me realize that I had a BIOS mis-configuration. Now 8 times 'cat /dev/zero > /dev/null &' on the ESXi host will result in 19199Mhz used which is 1Mhz from max!

Phey!

Sorry for 'craying wolf'!

PS: At least I got my knowledge of C- and P-CPU states refreshed! 🙂

Best regards,

- Morten Green Hermansen, Fanitas

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weinstein5
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Immortal

Remember there is CPU overhead for the ESXi host so that is why you will never be able to assign all CPU cycles to a VM - now on to the question why only 50% - how many virtual cpus does your vm have? I am assuming one - because a vcpu can only run on a single core at a time -

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mortengh
Enthusiast
Enthusiast

Hello weinstein5!

I assigned 7 vCPUs to the 8 pCPU system (left one to the hypervisor). But I ran 20 processes - 10 in the VM and 10 on the ESXi host itself.

This should max out the CPU usage would I mean.

Please see the screenshot below.

By starting 10 threads on the ESXi host I will max out all CPU cores.

Please note that CPU usage is exactly 11200Mhz... This is exactly 8 x 1.4Ghz... This is noteworthy!

Screen Shot 2015-03-27 at 21.16.06.png

Seems like the CPU is stalled in one of the ACPI power saving states. But I have 'high performance' as the active policy.

My other ESXi servers can run the blue bar all the way to 100% when CPU is maxed out.

Best regards,

- Morten Green Hermansen, Fanitas

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mortengh
Enthusiast
Enthusiast

Hello people!

Pressing 'p' in esxtop made me realize that I had a BIOS mis-configuration. Now 8 times 'cat /dev/zero > /dev/null &' on the ESXi host will result in 19199Mhz used which is 1Mhz from max!

Phey!

Sorry for 'craying wolf'!

PS: At least I got my knowledge of C- and P-CPU states refreshed! 🙂

Best regards,

- Morten Green Hermansen, Fanitas

View solution in original post

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