add WakeupEvents and Flush #188
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usamasaqib
reviewed
Jul 3, 2024
| @@ -127,7 +132,8 @@ func (m *PerfMap) Start() error { | |||
| // Create and start the perf map | |||
| var err error | |||
| opt := perf.ReaderOptions{ | |||
| Watermark: m.Watermark, | |||
| Watermark: m.Watermark, | |||
| WakeupEvents: m.WakeupEvents, | |||
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Should we just set one of these, to avoid confusions around which one gets applied by the kernel?
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Upstream handles if they are both set to non-zero values with an error https://github.com/cilium/ebpf/blob/f2b2f6d61aaf1fa8c0eb14c2a58f7e199fbd6086/perf/reader.go#L198-L200
usamasaqib
approved these changes
Jul 3, 2024
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What does this PR do?
Adds
WakeupEventsto perf buffers andFlushto both perf buffers and ring buffers.Motivation
WakeupEventsis used to queue data in perf buffers without waking up userspace. Ring buffers have this builtin control from the eBPF side with flags to helper calls.Flushis used to manually wakeup userspace to read any data already queued in the buffer. This is useful to have a synchronization point where you have read all available data.Additional Notes
A sentinel error
perf.ErrFlushedis reported by the upstream library when aFlushhas completed reading all available data. This is turned into aRecordwith an emptyRawSamplefield. This is so there is an in-band way of detecting the end. Using the error channel or something else would require potentially complex synchronization.Describe how to test your changes