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Recent patches to mlx5 mentioned a regression when moving from driver local page pool to only using the generic page pool code. Page pool has two recycling paths (1) direct one, which runs in safe NAPI context (basically consumer context, so producing can be lockless); and (2) via a ptr_ring, which takes a spin lock because the freeing can happen from any CPU; producer and consumer may run concurrently. Since the page pool code was added, Eric introduced a revised version of deferred skb freeing. TCP skbs are now usually returned to the CPU which allocated them, and freed in softirq context. This places the freeing (producing of pages back to the pool) enticingly close to the allocation (consumer). If we can prove that we're freeing in the same softirq context in which the consumer NAPI will run - lockless use of the cache is perfectly fine, no need for the lock. Let drivers link the page pool to a NAPI instance. If the NAPI instance is scheduled on the same CPU on which we're freeing - place the pages in the direct cache. With that and patched bnxt (XDP enabled to engage the page pool, sigh, bnxt really needs page pool work :() I see a 2.6% perf boost with a TCP stream test (app on a different physical core than softirq). The CPU use of relevant functions decreases as expected: page_pool_refill_alloc_cache 1.17% -> 0% _raw_spin_lock 2.41% -> 0.98% Only consider lockless path to be safe when NAPI is scheduled - in practice this should cover majority if not all of steady state workloads. It's usually the NAPI kicking in that causes the skb flush. The main case we'll miss out on is when application runs on the same CPU as NAPI. In that case we don't use the deferred skb free path. Reviewed-by: Tariq Toukan <tariqt@nvidia.com> Acked-by: Jesper Dangaard Brouer <brouer@redhat.com> Tested-by: Dragos Tatulea <dtatulea@nvidia.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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| .. | ||
| caif | ||
| device_drivers | ||
| devlink | ||
| dsa | ||
| mac80211_hwsim | ||
| 6lowpan.rst | ||
| 6pack.rst | ||
| af_xdp.rst | ||
| alias.rst | ||
| arcnet-hardware.rst | ||
| arcnet.rst | ||
| atm.rst | ||
| ax25.rst | ||
| bareudp.rst | ||
| batman-adv.rst | ||
| bonding.rst | ||
| bridge.rst | ||
| can_ucan_protocol.rst | ||
| can.rst | ||
| cdc_mbim.rst | ||
| checksum-offloads.rst | ||
| dccp.rst | ||
| dctcp.rst | ||
| dns_resolver.rst | ||
| driver.rst | ||
| eql.rst | ||
| ethtool-netlink.rst | ||
| failover.rst | ||
| fib_trie.rst | ||
| filter.rst | ||
| gen_stats.rst | ||
| generic_netlink.rst | ||
| generic-hdlc.rst | ||
| gtp.rst | ||
| ieee802154.rst | ||
| ila.rst | ||
| index.rst | ||
| ioam6-sysctl.rst | ||
| ip_dynaddr.rst | ||
| ip-sysctl.rst | ||
| ipddp.rst | ||
| ipsec.rst | ||
| ipv6.rst | ||
| ipvlan.rst | ||
| ipvs-sysctl.rst | ||
| j1939.rst | ||
| kapi.rst | ||
| kcm.rst | ||
| l2tp.rst | ||
| lapb-module.rst | ||
| mac80211-auth-assoc-deauth.txt | ||
| mac80211-injection.rst | ||
| mctp.rst | ||
| mpls-sysctl.rst | ||
| mptcp-sysctl.rst | ||
| msg_zerocopy.rst | ||
| multiqueue.rst | ||
| napi.rst | ||
| net_dim.rst | ||
| net_failover.rst | ||
| netconsole.rst | ||
| netdev-features.rst | ||
| netdevices.rst | ||
| netfilter-sysctl.rst | ||
| netif-msg.rst | ||
| nexthop-group-resilient.rst | ||
| nf_conntrack-sysctl.rst | ||
| nf_flowtable.rst | ||
| nfc.rst | ||
| openvswitch.rst | ||
| operstates.rst | ||
| packet_mmap.rst | ||
| page_pool.rst | ||
| phonet.rst | ||
| phy.rst | ||
| pktgen.rst | ||
| plip.rst | ||
| ppp_generic.rst | ||
| proc_net_tcp.rst | ||
| radiotap-headers.rst | ||
| rds.rst | ||
| regulatory.rst | ||
| representors.rst | ||
| rxrpc.rst | ||
| scaling.rst | ||
| sctp.rst | ||
| secid.rst | ||
| seg6-sysctl.rst | ||
| segmentation-offloads.rst | ||
| sfp-phylink.rst | ||
| skbuff.rst | ||
| smc-sysctl.rst | ||
| snmp_counter.rst | ||
| statistics.rst | ||
| strparser.rst | ||
| switchdev.rst | ||
| sysfs-tagging.rst | ||
| tc-actions-env-rules.rst | ||
| tc-queue-filters.rst | ||
| tcp-thin.rst | ||
| team.rst | ||
| timestamping.rst | ||
| tipc.rst | ||
| tls-offload-layers.svg | ||
| tls-offload-reorder-bad.svg | ||
| tls-offload-reorder-good.svg | ||
| tls-offload.rst | ||
| tls.rst | ||
| tproxy.rst | ||
| tuntap.rst | ||
| udplite.rst | ||
| vrf.rst | ||
| vxlan.rst | ||
| x25-iface.rst | ||
| x25.rst | ||
| xdp-rx-metadata.rst | ||
| xfrm_device.rst | ||
| xfrm_proc.rst | ||
| xfrm_sync.rst | ||
| xfrm_sysctl.rst | ||
