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Ignore unknown link speed in homa_qdev_update_sysctl - #23
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Drivers that don't know the link speed, such as virtio_net, report SPEED_UNKNOWN (-1) from get_link_ksettings. homa_qdev_update_sysctl used it as is, giving link_mbps -1 and a negative max_nic_queue_bytes, so every deferrable packet was deferred and the pacer never sent it: with the homa qdisc on a virtio NIC, large Homa messages and TCP stalled. A speed of 0 would divide by zero. Fall back to homa->link_mbps in both cases. Found by running two VMs with the homa qdisc on their virtio NICs. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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homa-qdisc (qdisc.nix) attaches Homa's qdisc to eth1 of each pair node. Pair lifecycle phases 10-12 run traffic through it, then with net.homa.link_mbps=1000 so the pacer must defer and send packets, then restore the default qdisc. New counters: qdisc_tcp_packets, pacer_homa_packets, pacer_tcp_packets. This reproduced round-4 candidate 5 in VMs: virtio-net reports SPEED_UNKNOWN, the qdisc takes link_mbps as -1, and echo, Homa and TCP all stall (STATUS.md F11). With the fix (fork #23) all 39 phases pass on 7.3 and 6.12, and homa-vm-matrix is 10/10. Also: echo output goes to a file (timeout's SIGTERM killed the grep in the pipeline), and cp_node counts as progressing when it reports a P99, since TCP's Kops at 5 % loss can round to 0.00. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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SPEED_UNKNOWN(-1) fromget_link_ksettings;homa_qdev_update_sysctlused it, givinglink_mbps-1 and a negativemax_nic_queue_bytes.pacer_homa_packets0).cycles_per_mibytecalculation.homa->link_mbpsfor 0 andSPEED_UNKNOWN.homa_qdev_update_sysctl__link_speed_unknown(red: link_mbps -1, cycles_per_mibyte 1953; green: 885/885).🤖 Generated with Claude Code