Design proposal for new ring buffer API #3848
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mikeagun
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dthaler,
poornagmsft,
Alan-Jowett,
saxena-anurag,
shankarseal,
dv-msft,
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matthewige,
mtfriesen and
rectified95
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mikeagun
changed the title
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Converting to draft while I make a few design updates. |
| * @returns Pointer to ring buffer manager. | ||
| */ | ||
| struct ring_buffer * | ||
| ring_buffer__new(int map_fd, ring_buffer_sample_fn sample_cb, void *ctx, |
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How do we differentiate between callback vs poll?
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Updated the design so callback consumers now use the libbpf ring buffer manager, and direct mapped memory consumers use the new functions.
docs/RingBuffer.md
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| // … log error … | ||
| break; | ||
| } | ||
| have_data = *prod_offset > *cons_offset; // It's possible we still have data. |
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You need a ReadAcquire here (or an explicit memory barrier). With out that, you can potentially read the record before its been written to by the producer. Likewise you will need a WriteRelease in the producer.
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Also, reading it multiple times like this is going to cause issues. It should read prod_offset once using ReadAcquire and then use the value.
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Now uses ReadAcquire64/WriteRelease64 for access to the producer and consumer offset.
I went with bit fields for the record header for simpler example code, so that part is already pseudocode and I didn't add the ReadAcquire needed to read the header, but added a comment in the struct.
Splits the design so callback consumers use the existing libbpf APIs, and mapped memory consumers use the new windows-specific functions.
docs/RingBuffer.md
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| // Update consumer offset (and pad record length to multiple of 8). | ||
| consumer_offset += sizeof(rb_header_t) + (record->length + 7 & ~7); | ||
| WriteRelease64(cons_offset, consumer_offset); |
Description
Add docs/RingBuffer.md with proposal for new ebpf ring buffer map API exposing mapped memory so consumers can directly read the records written by the producer (similar to linux mmap/epoll style ring buffer consumer).
Testing
N/A
Documentation
Documentation only.
Installation
N/A