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64 lines
3.0 KiB
Markdown
64 lines
3.0 KiB
Markdown
chroprof - Profiling for [Chronos](https://github.com/status-im/nim-chronos)
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============================================================================
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This repo contains a usable profiler for [Chronos](https://github.com/status-im/nim-chronos). For the time being, it requires [a modified version of Chronos V4](https://github.com/codex-storage/nim-chronos/tree/feature/profiler-v4) which has profiling hooks enabled. Some of the rationale for the design and implementation of the profiler [can be found here](https://hackmd.io/eQ_ouNV4QZe0TG334_gkFg).
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1. [Enabling profiling](#enabling-profiling)
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2. [Looking at metrics](#looking-at-metrics)
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2. [Enabling profiling with Prometheus metrics](#enabling-profiling-with-prometheus-metrics)
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3. [Limitations](#limitations)
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## Enabling Profiling
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**Compile-time flag.** Profiling requires the `-d:chronosProfiling` compile-time
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flag. If you do not pass it, importing `chroprof` will fail.
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**Enabling the profiler.** The profiler must be enabled per event loop thread.
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To enable it, you need to call, from the thread that will run your event loop:
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```nim
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import chroprof
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enableProfiling()
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```
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## Looking at Metrics
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At any time during execution, you can get a snapshot of the profiler metrics
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by calling `getMetrics()`. This will return a [`MetricsTotals`](https://github.com/codex-storage/nim-chroprof/blob/master/chroprof/profiler.nim#L61) object which
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is a table mapping [`FutureType`](https://github.com/codex-storage/nim-chroprof/blob/master/chroprof/profiler.nim#L13)s to
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[`AggregateMetrics`](https://github.com/codex-storage/nim-chroprof/blob/master/chroprof/profiler.nim#L17). You may then
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print, log, or do whatever you like with those, including [export them to Prometheus](#enabling-profiling-with-prometheus-metrics).
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`getMetrics()` will return the metrics for the event loop that is running
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(or ran) on the calling thread.
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## Enabling profiling with Prometheus metrics
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You can export metrics on the top-`k` async procs that are occupying the event
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loop thread the most by enabling the profiler's [nim-metrics](https://github.com/status-im/nim-metrics/) collector:
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```nim
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import chroprof/collector
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# Exports metrics for the 50 heaviest procs
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enableProfilerMetrics(50)
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```
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with the help of [Grafana](https://grafana.com/), one can visualize and readily identify bottlenecks:
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the cumulative chart on the left shows that two procs (with the bottom one
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turning out to be a child of the top one) were dominating execution time at a
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certain point, whereas the one on the right shows a number of peaks and anomalies
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which, in the context of a bug, may help identify the cause.
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## Limitations
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* Nested `waitFor` calls are not supported;
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* Prometheus metrics only work with `refc` because nim-metrics only works with `refc`;
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* the Prometheus metrics collector can only be enabled for one event loop; i.e.,
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you cannot have multiple loops in different threads publishing metrics to Prometheus.
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