finagle a STREAMS rx buffer size for DLPI handles - #1204
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Ran tests and a/b checks on 64KB vs 4MB. Softnpu hits "fast enough" that way, with uploads and |
This was referenced Aug 28, 2026
rcgoodfellow
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Aug 28, 2026
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| let mut offset = 1; | ||
| for de in &dir[msg.offset as usize..] { | ||
| for (offset, de) in (1..).zip(dir[msg.offset as usize..].iter()) { |
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Thsi is addressing a recent clippy complaint.
rcgoodfellow
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August 28, 2026 18:33
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STREAMS uses a high water mark as a back pressure mechanism. When we hit the high water mark, messages are dropped until we drain to the low water mark. This essentially makes the high water mark a receive buffer size.
For TCP on the STREAMS path (i.e. TPI consumers), it appears that the high water mark is set to SO_RCVBUF which is 128000 bytes. However, for DLPI the high water mark is not set and it defaults to 5120. This meaans we hit the mark at the first jumbo frame and thrash from there.
It seems the only way to influence this outside the kernel is pushing a passthrough bufmod STREAMS module. So that's what we do here for the time being.
It looks like the CI failure is addressed by #1093