Raise loop and chunk limit for newer kernels #1795
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Signed-off-by: Benjamin Kilimnik <bkilimnik@pixielabs.ai>
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Signed-off-by: Benjamin Kilimnik <bkilimnik@pixielabs.ai>
| Status SocketTraceConnector::InitBPF() { | ||
| // set BPF loop limit and chunk limit based on kernel version | ||
| auto kernel = system::GetCachedKernelVersion(); | ||
| int loop_limit = 42; |
Signed-off-by: Benjamin Kilimnik <bkilimnik@pixielabs.ai>
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etep
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Jan 18, 2024
JamesMBartlett
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Jan 23, 2024
| // Kernels >= 5.1 have higher BPF instruction limits (1 million for verifier). | ||
| // This enables a 21x increase to our loop and chunk limits | ||
| FLAGS_stirling_bpf_loop_limit = 882; | ||
| FLAGS_stirling_bpf_chunk_limit = 84; |
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How did you pick these numbers? How close are we to the instruction limit with these numbers?
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I manually raised the loop/chunk limits to see when the verifier would throw an error and chose values just below that upper bound, which is around 22x our previous limits.
bpf: Argument list too long. Program too large (... insns), at most 4096 insnsConfusingly, the bpf(2) syscall returns the same error whether the program size or its complexity exceeds the limits. See stackoverflow
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Summary: Dynamically increase the loop limit for newer kernels with higher instruction limits (1 million for kernels > 5.1) by 21x to reduce data loss and raise ingest. More details in #1755.
One open question is whether we want to add vizier flag to toggle this behavior in case there are unforseen performance bottlenecks for certain clusters.
Type of change: /kind feature
Test Plan: Existing targets + perf/demo tests outlined in #1755.