Date: Mon, 27 Apr 2026 19:48:18 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 294831] iflib clamps receive buffer to 4k causing jumbo frames to get dropped Message-ID: <bug-294831-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294831 Bug ID: 294831 Summary: iflib clamps receive buffer to 4k causing jumbo frames to get dropped Product: Base System Version: 15.0-RELEASE Hardware: amd64 OS: Any Status: New Severity: Affects Some People Priority: --- Component: bin Assignee: bugs@FreeBSD.org Reporter: pingpong7001@tutamail.com When using vmware workstation and enabling jumbo frames on the vmxnet3 driver, I appear to be dropping incomming frames with anything larger than an MTU of 4082 bytes. On investigation, it appear that the issue is dev.vmx.0.iflib.rxq0.rxq_fl1.buf_size gets clamped to 4096 (or 2048) in https://cgit.freebsd.org/src/tree/sys/net/iflib.c#n2448. I have a freebsd 14 box running on metal with a intel x550-t2 card, which using the ix driver which also appears to use iflib, but does not have this issue. I am wondering if it is something dumb like vmware workstation does not split those larger frames across receive decriptors natively and the nic does ? I am not an expert here, just an assumption. I updated iflib_get_mbuf_size_for to set the receive buffer size depending on what the MTU is. So with MTU of 9000, the buffer size gets set to 9216. static uint16_t iflib_get_mbuf_size_for(unsigned int size) { if (size <= MCLBYTES) return (MCLBYTES); else if (size <= MJUMPAGESIZE) return (MJUMPAGESIZE); else if (size <= MJUM9BYTES) return (MJUM9BYTES); else return (MJUM16BYTES); } I am not sure if this is the appropriate fix, or if there is a reason iflib clamps at 4k but it works for me, and thought this might be valuable to others if they are also hitting this. Is this something that you might want to roll into a fix going forward ? -- You are receiving this mail because: You are the assignee for the bug.home | help
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