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Update energy.md

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# Energy Saving # Energy Saving
Due to high energy prices and reductions in funding, we have implemented a set of energy saving measures at the IT4Innovations National Supercomputer Center. The measures are selected such as to minimize the performance impact and achieve significant cost, energy, and carbon footprint reduction effect. Due to high energy prices and reductions in funding, IT4Innovations has implemented a set of energy saving measures on the supercomputing clusters. The measures are selected to minimize the performance impact and achieve significant cost, energy, and carbon footprint reduction effect.
The energy saving measures are effective as of **1.2.2023**. The energy saving measures are effective as of **1.2.2023**.
...@@ -8,26 +8,26 @@ The energy saving measures are effective as of **1.2.2023**. ...@@ -8,26 +8,26 @@ The energy saving measures are effective as of **1.2.2023**.
### Measures ### Measures
Core frequency capping is implemented for the Karolina supercomputer: The CPU core and GPU streaming multiprocessors frequency limit is implemented for the Karolina supercomputer:
|Measure | Value | |Measure | Value |
|---------------------------------------------------------|---------| |---------------------------------------------------------|---------|
|Compute nodes **cn[001-720]**<br> CPU core frequency [capping][3] | 2.100 GHz | |Compute nodes **cn[001-720]**<br> CPU core frequency limit | 2.100 GHz |
|Accelerated compute nodes **acn[001-72]**<br> CPU core frequency capping | 2.600 GHz | |Accelerated compute nodes **acn[001-72]**<br> CPU core frequency limit | 2.600 GHz |
|Accelerated compute nodes **acn[001-72]**<br> GPU core frequency capping | 1.290 GHz | |Accelerated compute nodes **acn[001-72]**<br> GPU SMs frequency limit | 1.290 GHz |
### Performance Impact ### Performance Impact
The performance impact depends on the [arithmetic intensity][1] of the job. The performance impact depends on the [arithmetic intensity][1] of the executed workload.
The [arithmetic intensity][2] is a measure of floating-point operations (FLOPs) performed by a given code (or code section) relative to the amount of memory accesses (Bytes) that are required to support those operations. It is defined as a FLOP per Byte ratio (F/B). It is a characteristics of the particular computational algorithm. The [arithmetic intensity][2] is a measure of floating-point operations (FLOPs) performed by a given code (or code section) relative to the amount of memory accesses (Bytes) that are required to support those operations. It is defined as a FLOP per Byte ratio (F/B). Arithmetic intensity is a characteristic of the computational algorithm.
In general, the processor frequency capping has low performance impact for memory bound computations with intensity below the [ridge point][2]. For processor bound computations with intensity above the [ridge point][2], the impact is proportional to the frequency reduction. The processor frequency [capping][3] has low performance impact for memory bound computations (arithmetic intensity below the [ridge point][2]). For processor bound computations (arithmetic intensity above the [ridge point][2]), the impact is proportional to the frequency reduction.
On Karolina, relative time increase factor **up to 1.16** is observed for arithmeticaly intensive workloads on CPU and **up to 1.1** on GPU. **No slowdown** is observed for memory bound workloads. On Karolina, time increase **up to 16%** is observed for arithmeticaly intensive CPU workloads and **up to 10%** for intensive GPU workloads. **No slowdown** is observed for memory bound workloads.
### Energy Saved ### Energy Efficiency
The energy efficiency in floating point operations per energy unit is increased by up to 30% for CPU workloads, up to 25% for GPU workloads. The efficiency depends on the arithmetic intensity, however energy savings are always achieved. The energy efficiency in floating point operations per energy unit is increased by **up to 30%** for both the CPU and GPU workloads. The efficiency depends on the arithmetic intensity, however energy savings are always achieved.
## Barbora ## Barbora
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