From: Eric Dumazet Date: Thu, 6 Nov 2025 20:29:34 +0000 (+0000) Subject: net: fix napi_consume_skb() with alien skbs X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e20dfbad8aab2b7c72571ae3c3e2e646d6b04cb7;p=thirdparty%2Fkernel%2Flinux.git net: fix napi_consume_skb() with alien skbs There is a lack of NUMA awareness and more generally lack of slab caches affinity on TX completion path. Modern drivers are using napi_consume_skb(), hoping to cache sk_buff in per-cpu caches so that they can be recycled in RX path. Only use this if the skb was allocated on the same cpu, otherwise use skb_attempt_defer_free() so that the skb is freed on the original cpu. This removes contention on SLUB spinlocks and data structures. After this patch, I get ~50% improvement for an UDP tx workload on an AMD EPYC 9B45 (IDPF 200Gbit NIC with 32 TX queues). 80 Mpps -> 120 Mpps. Profiling one of the 32 cpus servicing NIC interrupts : Before: mpstat -P 511 1 1 Average: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle Average: 511 0.00 0.00 0.00 0.00 0.00 98.00 0.00 0.00 0.00 2.00 31.01% ksoftirqd/511 [kernel.kallsyms] [k] queued_spin_lock_slowpath 12.45% swapper [kernel.kallsyms] [k] queued_spin_lock_slowpath 5.60% ksoftirqd/511 [kernel.kallsyms] [k] __slab_free 3.31% ksoftirqd/511 [kernel.kallsyms] [k] idpf_tx_clean_buf_ring 3.27% ksoftirqd/511 [kernel.kallsyms] [k] idpf_tx_splitq_clean_all 2.95% ksoftirqd/511 [kernel.kallsyms] [k] idpf_tx_splitq_start 2.52% ksoftirqd/511 [kernel.kallsyms] [k] fq_dequeue 2.32% ksoftirqd/511 [kernel.kallsyms] [k] read_tsc 2.25% ksoftirqd/511 [kernel.kallsyms] [k] build_detached_freelist 2.15% ksoftirqd/511 [kernel.kallsyms] [k] kmem_cache_free 2.11% swapper [kernel.kallsyms] [k] __slab_free 2.06% ksoftirqd/511 [kernel.kallsyms] [k] idpf_features_check 2.01% ksoftirqd/511 [kernel.kallsyms] [k] idpf_tx_splitq_clean_hdr 1.97% ksoftirqd/511 [kernel.kallsyms] [k] skb_release_data 1.52% ksoftirqd/511 [kernel.kallsyms] [k] sock_wfree 1.34% swapper [kernel.kallsyms] [k] idpf_tx_clean_buf_ring 1.23% swapper [kernel.kallsyms] [k] idpf_tx_splitq_clean_all 1.15% ksoftirqd/511 [kernel.kallsyms] [k] dma_unmap_page_attrs 1.11% swapper [kernel.kallsyms] [k] idpf_tx_splitq_start 1.03% swapper [kernel.kallsyms] [k] fq_dequeue 0.94% swapper [kernel.kallsyms] [k] kmem_cache_free 0.93% swapper [kernel.kallsyms] [k] read_tsc 0.81% ksoftirqd/511 [kernel.kallsyms] [k] napi_consume_skb 0.79% swapper [kernel.kallsyms] [k] idpf_tx_splitq_clean_hdr 0.77% ksoftirqd/511 [kernel.kallsyms] [k] skb_free_head 0.76% swapper [kernel.kallsyms] [k] idpf_features_check 0.72% swapper [kernel.kallsyms] [k] skb_release_data 0.69% swapper [kernel.kallsyms] [k] build_detached_freelist 0.58% ksoftirqd/511 [kernel.kallsyms] [k] skb_release_head_state 0.56% ksoftirqd/511 [kernel.kallsyms] [k] __put_partials 0.55% ksoftirqd/511 [kernel.kallsyms] [k] kmem_cache_free_bulk 0.48% swapper [kernel.kallsyms] [k] sock_wfree After: mpstat -P 511 1 1 Average: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle Average: 511 0.00 0.00 0.00 0.00 0.00 51.49 0.00 0.00 0.00 48.51 19.10% swapper [kernel.kallsyms] [k] idpf_tx_splitq_clean_hdr 13.86% swapper [kernel.kallsyms] [k] idpf_tx_clean_buf_ring 10.80% swapper [kernel.kallsyms] [k] skb_attempt_defer_free 10.57% swapper [kernel.kallsyms] [k] idpf_tx_splitq_clean_all 7.18% swapper [kernel.kallsyms] [k] queued_spin_lock_slowpath 6.69% swapper [kernel.kallsyms] [k] sock_wfree 5.55% swapper [kernel.kallsyms] [k] dma_unmap_page_attrs 3.10% swapper [kernel.kallsyms] [k] fq_dequeue 3.00% swapper [kernel.kallsyms] [k] skb_release_head_state 2.73% swapper [kernel.kallsyms] [k] read_tsc 2.48% swapper [kernel.kallsyms] [k] idpf_tx_splitq_start 1.20% swapper [kernel.kallsyms] [k] idpf_features_check 1.13% swapper [kernel.kallsyms] [k] napi_consume_skb 0.93% swapper [kernel.kallsyms] [k] idpf_vport_splitq_napi_poll 0.64% swapper [kernel.kallsyms] [k] native_send_call_func_single_ipi 0.60% swapper [kernel.kallsyms] [k] acpi_processor_ffh_cstate_enter 0.53% swapper [kernel.kallsyms] [k] io_idle 0.43% swapper [kernel.kallsyms] [k] netif_skb_features 0.41% swapper [kernel.kallsyms] [k] __direct_call_cpuidle_state_enter2 0.40% swapper [kernel.kallsyms] [k] native_irq_return_iret 0.40% swapper [kernel.kallsyms] [k] idpf_tx_buf_hw_update 0.36% swapper [kernel.kallsyms] [k] sched_clock_noinstr 0.34% swapper [kernel.kallsyms] [k] handle_softirqs 0.32% swapper [kernel.kallsyms] [k] net_rx_action 0.32% swapper [kernel.kallsyms] [k] dql_completed 0.32% swapper [kernel.kallsyms] [k] validate_xmit_skb 0.31% swapper [kernel.kallsyms] [k] skb_network_protocol 0.29% swapper [kernel.kallsyms] [k] skb_csum_hwoffload_help 0.29% swapper [kernel.kallsyms] [k] x2apic_send_IPI 0.28% swapper [kernel.kallsyms] [k] ktime_get 0.24% swapper [kernel.kallsyms] [k] __qdisc_run Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Reviewed-by: Toke Høiland-Jørgensen Reviewed-by: Jason Xing Link: https://patch.msgid.link/20251106202935.1776179-3-edumazet@google.com Signed-off-by: Jakub Kicinski --- diff --git a/net/core/skbuff.c b/net/core/skbuff.c index eeddb9e737ff2..7ac5f8aa1235a 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1476,6 +1476,11 @@ void napi_consume_skb(struct sk_buff *skb, int budget) DEBUG_NET_WARN_ON_ONCE(!in_softirq()); + if (skb->alloc_cpu != smp_processor_id() && !skb_shared(skb)) { + skb_release_head_state(skb); + return skb_attempt_defer_free(skb); + } + if (!skb_unref(skb)) return;