https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=253069
Bug ID: 253069
Summary: cxgbe fl_pktshift not handled in netmap mode
Product: Base System
Version: 12.2-RELEASE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: b...@freebsd.org
Reporter: brian90...@gmail.com
Hello,
Today I tried using the hw.cxgbe.fl_pktshift sysctl to see if it would improve
the overall packet rate. I was using hw.cxgbe.fl_pktshift=2 to produce 4 byte
alignment with my Ethernet/IP data. After looking at the data, I realized the
Ethernet frames were not being recognized. I am using the cc0 interface in
netmap mode.
I captured packets from the interface and viewed them using tcpdump. It looks
like the pktshift is not being accounted for by the driver as the first two
byte are the EtherType from the Ethernet header.
17:42:12.555105 1a:84:9a:83:ca:44 > 00:00:8b:cb:f9:5d, ethertype Unknown
(0x268f), length 811:
0x0000: 0800 4500 031d 0001 0000 4011 07bd 8fdb
I reviewed the driver code and found this segment in eth_rx():
m0->m_pkthdr.len -= sc->params.sge.fl_pktshift;
m0->m_len -= sc->params.sge.fl_pktshift;
m0->m_data += sc->params.sge.fl_pktshift;
So the driver is transparently removing the shift from the length and the data
pointer. However, in service_nm_rxq() I see only:
case CPL_RX_PKT:
ring->slot[fl_cidx].len = G_RSPD_LEN(lq) -
sc->params.sge.fl_pktshift;
The length is being adjusted. However does the data pointer need adjusting as
well? Is this sysctl not supported while in netmap mode?
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