From 00596fdc29a4a3cf477b0ad00df9c328d6db6013 Mon Sep 17 00:00:00 2001 From: Andy Turner Date: Wed, 25 Oct 2023 08:12:45 +0100 Subject: [PATCH] Adds notes on frequency settings --- docs/user-guide/energy.md | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/docs/user-guide/energy.md b/docs/user-guide/energy.md index c0b702a61..fc9592e93 100644 --- a/docs/user-guide/energy.md +++ b/docs/user-guide/energy.md @@ -4,8 +4,8 @@ This section covers how to monitor energy use for your jobs on ARCHER2 and how t which allows some control over how much energy is consumed by jobs. !!! important - The default CPU frequency on ARCHER2 compute nodes for jobs launched using `srun` is currently set - to 2.0 GHz. Information below describes how to control the CPU frequency using Slurm. + The default CPU frequency cap on ARCHER2 compute nodes for jobs launched using `srun` is currently set + to 2.0 GHz. Information below describes how to control the CPU frequency cap using Slurm. ## Monitoring energy use @@ -87,8 +87,8 @@ There are a number of files in this directory, all the counter files include the ## Controlling CPU frequency -You can request specific CPU frequencies (in kHz) for compute nodes through `srun` options or environment variables. -The available frequencies on the ARCHER2 processors along with the options and environment variables: +You can request specific CPU frequency caps (in kHz) for compute nodes through `srun` options or environment variables. +The available frequency caps on the ARCHER2 processors along with the options and environment variables: | Frequency | `srun` option | Slurm environment variable | Turbo boost enabled? | |----------:|--------------|----------------------------|-------| @@ -96,7 +96,18 @@ The available frequencies on the ARCHER2 processors along with the options and e | 2.00 GHz | `--cpu-freq=2000000` | `export SLURM_CPU_FREQ_REQ=2000000` | No | | 1.50 GHz | `--cpu-freq=1500000` | `export SLURM_CPU_FREQ_REQ=1500000` | No | -The only frequencies available on the processors on ARCHER2 are 1.5 GHz, 2.0 GHz and 2.25GHz. +The only frequency caps available on the processors on ARCHER2 are 1.5 GHz, 2.0 GHz and 2.25GHz+turbo. + +!!! important + Setting the CPU frequency cap in this way sets the *maximum* frequency that the processors can use. + In practice, the individual cores may select different frequencies up to the value you have set depending + on the workload on the processor. + +!!! important + When you select the highest frequency value (2.25 GHz), you also enable turbo boost and so + the processor is free to set the CPU frequency to values above 2.25 GHz if possible within + the power and thermal limits of the processor. We see that, with turbo boost enabled, + the processors typically boost to around 2.8 GHz even when performing compute-intensive work. For example, you can add the following option to `srun` commands in your job submission scripts to set the CPU frequency to 2.25 GHz (and also enable turbo boost):