4 ms·

Disable hyperthreading, it's overrated anyways

by gfody 9y ago

shmerl 9y ago
Is it? I know there are workloads when it actually can hurt performance, but are they more common than ones when it helps?
- Symmetry 9y ago
  Here's Anandtech's recent SPEC benchmark deltas on hypertheading. http://www.anandtech.com/show/11544/intel-skylake-ep-vs-amd-epyc-7000-cpu-battle-of-the-decade/15 http://www.anandtech.com/show/11544/intel-skylake-ep-vs-amd-...
  - shmerl 9y ago
    I see performance increases in every row there, so it must be beneficial in most cases.
    - gfody 9y ago
      comparing single threaded performance vs. two-threads-on-one-core will do that. here's a bunch of real-world tests (mostly gaming) showing HT hurting performance: https://www.techpowerup.com/forums/threads/gaming-benchmarks-core-i7-6700k-hyperthreading-test.219417 https://www.techpowerup.com/forums/threads/gaming-benchmarks...
- loeg 9y ago
  It's not net helpful if it triggers a CPU bug.
  - shmerl 9y ago
    Sure, but if it's a feature that's increasing performance without a bug, it's something that should be fixed, otherwise you are paying for broken hardware.
- Sohcahtoa82 9y ago
  > I know there are workloads when it actually can hurt performance From what I've seen, performance is only hurt in contrived benchmarks intended to cause slowdowns when HT is in use.
- zrm 9y ago
  > I know there are workloads when it actually can hurt performance, but are they more common than ones when it helps? Hyperthreading makes better use of execution units but causes twice as many threads to share memory bandwidth and caches. It's often a good trade-off. But it's also less valuable for high core-count processors, because workloads that aren't highly parallel will have idle real cores to run other threads on, and highly parallel workloads are more likely to be bottlenecked by memory and caches when there are more cores. The real question is whether it's faster for your workload. And your hardware. The answer could be different on a system with 8 cores and 2 memory channels than a system with 4 cores and 4 memory channels. Turn it on and then off and see which is faster for you.

Disable hyperthreading, it's overrated anyways

by gfody 9y ago

Disable hyperthreading, it's overrated anyways

Is it? I know there are workloads when it actually can hurt performance, but are they more common than ones when it helps?

Symmetry 9y ago
Here's Anandtech's recent SPEC benchmark deltas on hypertheading. http://www.anandtech.com/show/11544/intel-skylake-ep-vs-amd-epyc-7000-cpu-battle-of-the-decade/15 http://www.anandtech.com/show/11544/intel-skylake-ep-vs-amd-...
- shmerl 9y ago
  I see performance increases in every row there, so it must be beneficial in most cases.
  - gfody 9y ago
    comparing single threaded performance vs. two-threads-on-one-core will do that. here's a bunch of real-world tests (mostly gaming) showing HT hurting performance: https://www.techpowerup.com/forums/threads/gaming-benchmarks-core-i7-6700k-hyperthreading-test.219417 https://www.techpowerup.com/forums/threads/gaming-benchmarks...
loeg 9y ago
It's not net helpful if it triggers a CPU bug.
- shmerl 9y ago
  Sure, but if it's a feature that's increasing performance without a bug, it's something that should be fixed, otherwise you are paying for broken hardware.
Sohcahtoa82 9y ago
> I know there are workloads when it actually can hurt performance From what I've seen, performance is only hurt in contrived benchmarks intended to cause slowdowns when HT is in use.
zrm 9y ago
> I know there are workloads when it actually can hurt performance, but are they more common than ones when it helps? Hyperthreading makes better use of execution units but causes twice as many threads to share memory bandwidth and caches. It's often a good trade-off. But it's also less valuable for high core-count processors, because workloads that aren't highly parallel will have idle real cores to run other threads on, and highly parallel workloads are more likely to be bottlenecked by memory and caches when there are more cores. The real question is whether it's faster for your workload. And your hardware. The answer could be different on a system with 8 cores and 2 memory channels than a system with 4 cores and 4 memory channels. Turn it on and then off and see which is faster for you.