46
votes
Accepted
Why did disabling hyperthreading make my server slower?
Your Ruby program did not use 2x the CPU time when running with HT disabled. Rather, as it maximizes one core out of two total cores, gnome-system-monitor will report as the utilization as 50%. If, ...
- 47.9k
31
votes
Disable hyperthreading from within Linux (no access to BIOS)
Newer Kernels provide a Simultaneous Multithreading (SMT) control.
You can check the state of SMT with;
cat /sys/devices/system/cpu/smt/active
Change the state with
echo off | sudo tee /sys/devices/...
23
votes
How many CPUs should be utilised with Hyperthreading?
CPU meters are very bad for telling you how much more performance you can squeeze out of your hyperthreaded CPUs. For that, you should run your own benchmarks at various physical-core over-...
- 133k
15
votes
Accepted
How many CPUs should be utilised with Hyperthreading?
If the second virtual core is allowed to contribute when the first would otherwise be stuck, it's better than not, so you get (at least) a little extra work done.
The question becomes: when does ...
- 296
14
votes
Disable hyperthreading from within Linux (no access to BIOS)
A script to disable hyperthreading in the machine startup...
To disable hyperthreading I include a script on machine /etc/rc.local. It is not exaclty clean, but is easy to install, independent of cpu ...
- 523
10
votes
Disable hyperthreading from within Linux (no access to BIOS)
You can use the "thread_siblings_list" for each core to turn off the second core in the HT pair.
The following command pipeline is hacky, not optimised, and done this way hopefully to make it easier ...
- 583
7
votes
Accepted
KVM: Which CPU for VM ('host' vs 'kvm64') to use for web load?
The Proxmox wiki addresses the issue of which CPU type to choose, in part:
Qemu can emulate a number different of CPU types from 486 to the latest Xeon processors. Each new processor generation adds ...
- 244k
7
votes
Accepted
Turning off HyperThread by BIOS or kernel?
Well, the first obvious difference is that noht doesn't actually do anything on modern Linux systems. This kernel boot option is long obsolete, and was replaced with maxcpus=.
Setting maxcpus=m, ...
- 244k
6
votes
Disable hyperthreading from within Linux (no access to BIOS)
Disable SMT / HT at boot time using the kernel command line parameter nosmt:
nosmt [KNL,S390] Disable symmetric multithreading (SMT).
Equivalent to smt=1.
...
- 161
6
votes
Accepted
AWS EC2 instance hyperthreading
I received confirmation from Amazon that a vCPU is in fact a single hyperthread on a single core.
On a side note, this was news to the software vendor we were working with (one of the biggest ...
- 211
4
votes
Disable hyperthreading from within Linux (no access to BIOS)
Lukas' answer is nice but does not really work for disabling HT because core ID cannot serve for identification of HT siblings. This script works instead:
#!/bin/bash
for CPU in /sys/devices/system/...
- 141
4
votes
How many CPUs should be utilised with Hyperthreading?
You should see all 36 cores running at 100 % - assuming the software can do that (which is not trivial - scheduling can be tricky with that many cores, so dips below 100% are acceptable).
Obviously ...
- 51.7k
4
votes
How vCPUs are calculated?
Your vendor is selling you a simple story to explain something that can be complicated, but theirs is a bit off.
For starters: Hyper Threading does not give you extra cores, it just abstracts task ...
- 68.9k
3
votes
ESXi hyper threading numbering for affinity settings
Why would you disable hyperthreading? It's in direct contravention to VMware's Performance Guidelines.
Anyway you've got the numbering wrong - with HT enabled CPU 0, core 0, thread 0 is seen by ESXi ...
- 101k
3
votes
How many CPUs should be utilised with Hyperthreading?
The way hyperthreading is implemented varies with the specific CPU uarch. From Nehalem to Skylake, Intel significantly reduced the fixed-ratio (ie: 50/50) shared parts of the pipeline, heading to ...
- 47.9k
3
votes
Accepted
EC2, Windows 10, half of the virtual processors
This issue happens when Hyper-Threading is disabled at OS level. This may have been done based on Microsoft recommendation for protecting against a known vulnerability known as speculative execution ...
- 96
3
votes
Why did disabling hyperthreading make my server slower?
I wanted to see if disabling hyperthreading benefits a programming language that runs on single thread.
I don't know how cutting the number of cores would improve performance, even for a single ...
- 661
3
votes
What performance statistics can I use to determine if hyperthreading will improve performance?
I can't tell if you're too academic in approach, but for most workloads on modern CPUs, people recommend leaving hypertheading on.
Now, given that you haven't provided details like the application ...
- 197k
2
votes
Accepted
Maria Performance Tuning: HyperThreading is great for marketing, lousy for performance
In my experience, MySQL/MariaDB do not need much CPU. Hence HyperThreading (etc) are not very important in the performance question. Usually, heavy CPU usage is readily cured by
Improving the ...
- 2,463
2
votes
KVM: Which CPU for VM ('host' vs 'kvm64') to use for web load?
For best performance host is the best option, as if the cpu has VT-x flag, it will directly be used within the virtual machine. Nothing needs to be emulated on the cpu and emulation has overhead.
The ...
- 71
1
vote
Benefits of hyperthreading for multiprocessing?
Bad analogy: Hyper-Threading, or in general SMT, is like a time-share vacation property. Scheduling all 52 weeks of the year is fine, everyone gets the place to themselves. Get a couple more people in ...
- 32.1k
1
vote
Benefits of hyperthreading for multiprocessing?
Simplified hyper threading takes advantage of the fact that in many process threads there is idle time when the core would normally be waiting for other tasks to complete. By switching between two ...
- 5,825
1
vote
Accepted
How to properly configure ESX VMs to use hyper threading in a usefull way?
Your problem is not HT. 50% HT boost is a number based on nothing. Usually, it can be 5-20% boost to some multi-threaded applications depending on the code and the workload. The point is you should ...
- 3,076
1
vote
Enabling Hyperthreading on a Centos 7.3 server using Intel Xeon E5620
Please enable Hyperthreading in the system ROM or BIOS utility.
Depending on the server solution, this needs to be done before the system boots.
- 197k
1
vote
What performance statistics can I use to determine if hyperthreading will improve performance?
As running experiments in a production environment is a poor idea
No it's not. Creating a realistic simulation of your live environment will cost you about as much as your total expenditure on your ...
- 21.3k
1
vote
VMware / SQL - physical vs logical cores - how many vCPUs to assign when HT is enabled
Generally, keeping assigned vCPUs no more than the physical cores (ignoring HT) is playing it safe. You have 2 physical CPUs with 8 core each (although I remember the E5-2667 having 6) - that means 16 ...
- 3,076
1
vote
Nginx worker_processes and multi core cpu's - Do Hyper-threading cores count?
As of today, you can configure both worker_process and worker_cpu_affinity to auto and it will handle automatically.
1
vote
Should I disable hyperthreading?
Slurm allocates by cores, SLURM was designed for portability not performance. So the way it allocates is "Note that even on systems with hyperthreading enabled, the resources will generally be ...
- 24.1k
1
vote
Should I disable hyperthreading?
Basically, if you feel that your operations would benefit from the freer L2/L3 cache that is possible when HT is disabled, go ahead and disable HT from the BIOS.
If however there is a large number of ...
- 41
1
vote
CPU parking, windows 2012r2, with no hyper threading
The PowerCfg commands will disable opportunistic core parking. If the server’s firmware uses the logical processor idling interface to request that Windows park cores, they would still be parked ...
- 11
Only top scored, non community-wiki answers of a minimum length are eligible