6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Krishna Kumar krikku@gmail.com
[ Upstream commit 5d3bc9e5e725aa36cca9b794e340057feb6880b4 ]
This patch fixes an issue seen in a large-scale deployment under heavy incoming pkts where the aRFS flow wrongly matches a flow and reprograms the NIC with wrong settings. That mis-steering causes RX-path latency spikes and noisy neighbor effects when many connections collide on the same hash (some of our production servers have 20-30K connections).
set_rps_cpu() calls ndo_rx_flow_steer() with flow_id that is calculated by hashing the skb sized by the per rx-queue table size. This results in multiple connections (even across different rx-queues) getting the same hash value. The driver steer function modifies the wrong flow to use this rx-queue, e.g.: Flow#1 is first added: Flow#1: <ip1, port1, ip2, port2>, Hash 'h', q#10
Later when a new flow needs to be added: Flow#2: <ip3, port3, ip4, port4>, Hash 'h', q#20
The driver finds the hash 'h' from Flow#1 and updates it to use q#20. This results in both flows getting un-optimized - packets for Flow#1 goes to q#20, and then reprogrammed back to q#10 later and so on; and Flow #2 programming is never done as Flow#1 is matched first for all misses. Many flows may wrongly share the same hash and reprogram rules of the original flow each with their own q#.
Tested on two 144-core servers with 16K netperf sessions for 180s. Netperf clients are pinned to cores 0-71 sequentially (so that wrong packets on q#s 72-143 can be measured). IRQs are set 1:1 for queues -> CPUs, enable XPS, enable aRFS (global value is 144 * rps_flow_cnt).
Test notes about results from ice_rx_flow_steer(): --------------------------------------------------- 1. "Skip:" counter increments here: if (fltr_info->q_index == rxq_idx || arfs_entry->fltr_state != ICE_ARFS_ACTIVE) goto out; 2. "Add:" counter increments here: ret = arfs_entry->fltr_info.fltr_id; INIT_HLIST_NODE(&arfs_entry->list_entry); 3. "Update:" counter increments here: /* update the queue to forward to on an already existing flow */
Runtime comparison: original code vs with the patch for different rps_flow_cnt values.
+-------------------------------+--------------+--------------+ | rps_flow_cnt | 512 | 2048 | +-------------------------------+--------------+--------------+ | Ratio of Pkts on Good:Bad q's | 214 vs 822K | 1.1M vs 980K | | Avoid wrong aRFS programming | 0 vs 310K | 0 vs 30K | | CPU User | 216 vs 183 | 216 vs 206 | | CPU System | 1441 vs 1171 | 1447 vs 1320 | | CPU Softirq | 1245 vs 920 | 1238 vs 961 | | CPU Total | 29 vs 22.7 | 29 vs 24.9 | | aRFS Update | 533K vs 59 | 521K vs 32 | | aRFS Skip | 82M vs 77M | 7.2M vs 4.5M | +-------------------------------+--------------+--------------+
A separate TCP_STREAM and TCP_RR with 1,4,8,16,64,128,256,512 connections showed no performance degradation.
Some points on the patch/aRFS behavior: 1. Enabling full tuple matching ensures flows are always correctly matched, even with smaller hash sizes. 2. 5-6% drop in CPU utilization as the packets arrive at the correct CPUs and fewer calls to driver for programming on misses. 3. Larger hash tables reduces mis-steering due to more unique flow hashes, but still has clashes. However, with larger per-device rps_flow_cnt, old flows take more time to expire and new aRFS flows cannot be added if h/w limits are reached (rps_may_expire_flow() succeeds when 10*rps_flow_cnt pkts have been processed by this cpu that are not part of the flow).
Fixes: 28bf26724fdb0 ("ice: Implement aRFS") Signed-off-by: Krishna Kumar krikku@gmail.com Reviewed-by: Simon Horman horms@kernel.org Tested-by: Rinitha S sx.rinitha@intel.com (A Contingent worker at Intel) Signed-off-by: Tony Nguyen anthony.l.nguyen@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ethernet/intel/ice/ice_arfs.c | 48 +++++++++++++++++++++++ 1 file changed, 48 insertions(+)
diff --git a/drivers/net/ethernet/intel/ice/ice_arfs.c b/drivers/net/ethernet/intel/ice/ice_arfs.c index d7e0116f67737..7036070bc0208 100644 --- a/drivers/net/ethernet/intel/ice/ice_arfs.c +++ b/drivers/net/ethernet/intel/ice/ice_arfs.c @@ -376,6 +376,50 @@ ice_arfs_is_perfect_flow_set(struct ice_hw *hw, __be16 l3_proto, u8 l4_proto) return false; }
+/** + * ice_arfs_cmp - Check if aRFS filter matches this flow. + * @fltr_info: filter info of the saved ARFS entry. + * @fk: flow dissector keys. + * @n_proto: One of htons(ETH_P_IP) or htons(ETH_P_IPV6). + * @ip_proto: One of IPPROTO_TCP or IPPROTO_UDP. + * + * Since this function assumes limited values for n_proto and ip_proto, it + * is meant to be called only from ice_rx_flow_steer(). + * + * Return: + * * true - fltr_info refers to the same flow as fk. + * * false - fltr_info and fk refer to different flows. + */ +static bool +ice_arfs_cmp(const struct ice_fdir_fltr *fltr_info, const struct flow_keys *fk, + __be16 n_proto, u8 ip_proto) +{ + /* Determine if the filter is for IPv4 or IPv6 based on flow_type, + * which is one of ICE_FLTR_PTYPE_NONF_IPV{4,6}_{TCP,UDP}. + */ + bool is_v4 = fltr_info->flow_type == ICE_FLTR_PTYPE_NONF_IPV4_TCP || + fltr_info->flow_type == ICE_FLTR_PTYPE_NONF_IPV4_UDP; + + /* Following checks are arranged in the quickest and most discriminative + * fields first for early failure. + */ + if (is_v4) + return n_proto == htons(ETH_P_IP) && + fltr_info->ip.v4.src_port == fk->ports.src && + fltr_info->ip.v4.dst_port == fk->ports.dst && + fltr_info->ip.v4.src_ip == fk->addrs.v4addrs.src && + fltr_info->ip.v4.dst_ip == fk->addrs.v4addrs.dst && + fltr_info->ip.v4.proto == ip_proto; + + return fltr_info->ip.v6.src_port == fk->ports.src && + fltr_info->ip.v6.dst_port == fk->ports.dst && + fltr_info->ip.v6.proto == ip_proto && + !memcmp(&fltr_info->ip.v6.src_ip, &fk->addrs.v6addrs.src, + sizeof(struct in6_addr)) && + !memcmp(&fltr_info->ip.v6.dst_ip, &fk->addrs.v6addrs.dst, + sizeof(struct in6_addr)); +} + /** * ice_rx_flow_steer - steer the Rx flow to where application is being run * @netdev: ptr to the netdev being adjusted @@ -447,6 +491,10 @@ ice_rx_flow_steer(struct net_device *netdev, const struct sk_buff *skb, continue;
fltr_info = &arfs_entry->fltr_info; + + if (!ice_arfs_cmp(fltr_info, &fk, n_proto, ip_proto)) + continue; + ret = fltr_info->fltr_id;
if (fltr_info->q_index == rxq_idx ||