Hi Mark,
I think this patch is going in the right direction but there are some points that I think we should address. See below. On Fri, Apr 30, 2021 at 11:33:25AM -0400, Mark Gray wrote: > The Open vSwitch kernel module uses the upcall mechanism to send > packets from kernel space to user space when it misses in the kernel > space flow table. The upcall sends packets via a Netlink socket. > Currently, a Netlink socket is created for every vport. In this way, > there is a 1:1 mapping between a vport and a Netlink socket. > When a packet is received by a vport, if it needs to be sent to > user space, it is sent via the corresponding Netlink socket. > > This mechanism, with various iterations of the corresponding user > space code, has seen some limitations and issues: > > * On systems with a large number of vports, there is a correspondingly > large number of Netlink sockets which can limit scaling. > (https://bugzilla.redhat.com/show_bug.cgi?id=1526306) > * Packet reordering on upcalls. > (https://bugzilla.redhat.com/show_bug.cgi?id=1844576) > * A thundering herd issue. > (https://bugzilla.redhat.com/show_bug.cgi?id=1834444) > > This patch introduces an alternative, feature-negotiated, upcall > mode using a per-cpu dispatch rather than a per-vport dispatch. > > In this mode, the Netlink socket to be used for the upcall is > selected based on the CPU of the thread that is executing the upcall. > In this way, it resolves the issues above as: > > a) The number of Netlink sockets scales with the number of CPUs > rather than the number of vports. > b) Ordering per-flow is maintained as packets are distributed to > CPUs based on mechanisms such as RSS and flows are distributed > to a single user space thread. > c) Packets from a flow can only wake up one user space thread. > > The corresponding user space code can be found at: > https://mail.openvswitch.org/pipermail/ovs-dev/2021-April/382618.html Thanks for writing a nice commit description. > > Bugzilla: https://bugzilla.redhat.com/1844576 > Signed-off-by: Mark Gray <mark.d.g...@redhat.com> > --- > include/uapi/linux/openvswitch.h | 8 ++++ > net/openvswitch/datapath.c | 70 +++++++++++++++++++++++++++++++- > net/openvswitch/datapath.h | 18 ++++++++ > net/openvswitch/flow_netlink.c | 4 -- > 4 files changed, 94 insertions(+), 6 deletions(-) > > diff --git a/include/uapi/linux/openvswitch.h > b/include/uapi/linux/openvswitch.h > index 8d16744edc31..6571b57b2268 100644 > --- a/include/uapi/linux/openvswitch.h > +++ b/include/uapi/linux/openvswitch.h > @@ -70,6 +70,8 @@ enum ovs_datapath_cmd { > * set on the datapath port (for OVS_ACTION_ATTR_MISS). Only valid on > * %OVS_DP_CMD_NEW requests. A value of zero indicates that upcalls should > * not be sent. > + * OVS_DP_ATTR_PER_CPU_PIDS: Per-cpu array of PIDs for upcalls when > + * OVS_DP_F_DISPATCH_UPCALL_PER_CPU feature is set. > * @OVS_DP_ATTR_STATS: Statistics about packets that have passed through the > * datapath. Always present in notifications. > * @OVS_DP_ATTR_MEGAFLOW_STATS: Statistics about mega flow masks usage for > the > @@ -87,6 +89,9 @@ enum ovs_datapath_attr { > OVS_DP_ATTR_USER_FEATURES, /* OVS_DP_F_* */ > OVS_DP_ATTR_PAD, > OVS_DP_ATTR_MASKS_CACHE_SIZE, > + OVS_DP_ATTR_PER_CPU_PIDS, /* Netlink PIDS to receive upcalls in > per-cpu > + * dispatch mode > + */ > __OVS_DP_ATTR_MAX > }; > > @@ -127,6 +132,9 @@ struct ovs_vport_stats { > /* Allow tc offload recirc sharing */ > #define OVS_DP_F_TC_RECIRC_SHARING (1 << 2) > > +/* Allow per-cpu dispatch of upcalls */ > +#define OVS_DP_F_DISPATCH_UPCALL_PER_CPU (1 << 3) > + > /* Fixed logical ports. */ > #define OVSP_LOCAL ((__u32)0) > > diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c > index 9d6ef6cb9b26..98d54f41fdaa 100644 > --- a/net/openvswitch/datapath.c > +++ b/net/openvswitch/datapath.c > @@ -121,6 +121,8 @@ int lockdep_ovsl_is_held(void) > #endif > > static struct vport *new_vport(const struct vport_parms *); > +static u32 ovs_dp_get_upcall_portid(const struct datapath *, uint32_t); > +static int ovs_dp_set_upcall_portids(struct datapath *, const struct nlattr > *); > static int queue_gso_packets(struct datapath *dp, struct sk_buff *, > const struct sw_flow_key *, > const struct dp_upcall_info *, > @@ -238,7 +240,12 @@ void ovs_dp_process_packet(struct sk_buff *skb, struct > sw_flow_key *key) > > memset(&upcall, 0, sizeof(upcall)); > upcall.cmd = OVS_PACKET_CMD_MISS; > - upcall.portid = ovs_vport_find_upcall_portid(p, skb); > + > + if (dp->user_features & OVS_DP_F_DISPATCH_UPCALL_PER_CPU) > + upcall.portid = ovs_dp_get_upcall_portid(dp, > smp_processor_id()); > + else > + upcall.portid = ovs_vport_find_upcall_portid(p, skb); > + We don't expect that to change during packet processing, so I wondered if that could be improved. However, user_feature is in the same cache line as stats_percpu which is also used. > upcall.mru = OVS_CB(skb)->mru; > error = ovs_dp_upcall(dp, skb, key, &upcall, 0); > if (unlikely(error)) > @@ -1590,16 +1597,67 @@ static void ovs_dp_reset_user_features(struct sk_buff > *skb, > > DEFINE_STATIC_KEY_FALSE(tc_recirc_sharing_support); > > +static int ovs_dp_set_upcall_portids(struct datapath *dp, > + const struct nlattr *ids) > +{ > + struct dp_portids *old, *dp_portids; > + > + if (!nla_len(ids) || nla_len(ids) % sizeof(u32)) > + return -EINVAL; > + > + old = ovsl_dereference(dp->upcall_portids); > + > + dp_portids = kmalloc(sizeof(*dp_portids) + nla_len(ids), > + GFP_KERNEL); > + if (!dp) I suspect you meant dp_portids. > + return -ENOMEM; > + > + dp_portids->n_ids = nla_len(ids) / sizeof(u32); > + nla_memcpy(dp_portids->ids, ids, nla_len(ids)); > + > + rcu_assign_pointer(dp->upcall_portids, dp_portids); > + > + if (old) > + kfree_rcu(old, rcu); IIRC, the kfree_rcu() checks for NULL pointers. > + return 0; > +} > + > +static u32 ovs_dp_get_upcall_portid(const struct datapath *dp, uint32_t > cpu_id) > +{ > + struct dp_portids *dp_portids; > + > + dp_portids = rcu_dereference_ovsl(dp->upcall_portids); > + > + if (dp->user_features & OVS_DP_F_DISPATCH_UPCALL_PER_CPU && dp_portids) > { The OVS_DP_F_DISPATCH_UPCALL_PER_CPU needs to be verified by the caller to decide whether to use this function or ovs_vport_find_upcall_portid(), so perhaps function could check only if dp_portids is set. > + if (cpu_id < dp_portids->n_ids) { > + return dp_portids->ids[cpu_id]; > + } else if (dp_portids->n_ids > 0 && cpu_id >= > dp_portids->n_ids) { > + /* If the number of netlink PIDs is mismatched with the > number of > + * CPUs as seen by the kernel, log this and send the > upcall to an > + * arbitrary socket (0) in order to not drop packets > + */ > + pr_info_ratelimited("cpu_id mismatch with handler > threads"); > + return dp_portids->ids[0]; Instead of returning a fixed pid for all other unmapped CPUs, perhaps it could distribute among mapped ones to help with the load: return dp_portids->ids[cpu_id % dp_portids->n_ids] > + } else { > + return 0; > + } > + } else { > + return 0; > + } > +} > + > static int ovs_dp_change(struct datapath *dp, struct nlattr *a[]) > { > u32 user_features = 0; > + int err; > > if (a[OVS_DP_ATTR_USER_FEATURES]) { > user_features = nla_get_u32(a[OVS_DP_ATTR_USER_FEATURES]); > > if (user_features & ~(OVS_DP_F_VPORT_PIDS | > OVS_DP_F_UNALIGNED | > - OVS_DP_F_TC_RECIRC_SHARING)) > + OVS_DP_F_TC_RECIRC_SHARING | > + OVS_DP_F_DISPATCH_UPCALL_PER_CPU)) > return -EOPNOTSUPP; > > #if !IS_ENABLED(CONFIG_NET_TC_SKB_EXT) > @@ -1620,6 +1678,14 @@ static int ovs_dp_change(struct datapath *dp, struct > nlattr *a[]) > > dp->user_features = user_features; > > + if (dp->user_features & OVS_DP_F_DISPATCH_UPCALL_PER_CPU && > + a[OVS_DP_ATTR_PER_CPU_PIDS]) { > + /* Upcall Netlink Port IDs have been updated */ > + err = ovs_dp_set_upcall_portids(dp, > a[OVS_DP_ATTR_PER_CPU_PIDS]); > + if (err) > + return err; > + } It is possible to switch between per_cpu_pids and per_ports_pids and vice versa. It seems this patch doesn't count for that. > + > if (dp->user_features & OVS_DP_F_TC_RECIRC_SHARING) > static_branch_enable(&tc_recirc_sharing_support); > else > diff --git a/net/openvswitch/datapath.h b/net/openvswitch/datapath.h > index 38f7d3e66ca6..6003eba81958 100644 > --- a/net/openvswitch/datapath.h > +++ b/net/openvswitch/datapath.h > @@ -50,6 +50,21 @@ struct dp_stats_percpu { > struct u64_stats_sync syncp; > }; > > +/** > + * struct dp_portids - array of netlink portids of for a datapath. > + * This is used when OVS_DP_F_DISPATCH_UPCALL_PER_CPU > + * is enabled and must be protected by rcu. > + * @rcu: RCU callback head for deferred destruction. > + * @n_ids: Size of @ids array. > + * @ids: Array storing the Netlink socket PIDs indexed by CPU ID for packets > + * that miss the flow table. > + */ > +struct dp_portids { > + struct rcu_head rcu; > + u32 n_ids; > + u32 ids[]; > +}; It doesn't have any relation to ports, so the name is somewhat misleading and confusing with the existing one. What do you think about the suggestion below: struct dp_nlsk_pids { struct rcu_head rcu; u32 n_pids; u32 pids[]; }; > + > /** > * struct datapath - datapath for flow-based packet switching > * @rcu: RCU callback head for deferred destruction. > @@ -61,6 +76,7 @@ struct dp_stats_percpu { > * @net: Reference to net namespace. > * @max_headroom: the maximum headroom of all vports in this datapath; it > will > * be used by all the internal vports in this dp. > + * @upcall_portids: RCU protected 'struct dp_portids'. > * > * Context: See the comment on locking at the top of datapath.c for > additional > * locking information. > @@ -87,6 +103,8 @@ struct datapath { > > /* Switch meters. */ > struct dp_meter_table meter_tbl; > + > + struct dp_portids __rcu *upcall_portids; > }; > > /** > diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c > index fd1f809e9bc1..97242bc1d960 100644 > --- a/net/openvswitch/flow_netlink.c > +++ b/net/openvswitch/flow_netlink.c > @@ -2928,10 +2928,6 @@ static int validate_userspace(const struct nlattr > *attr) > if (error) > return error; > > - if (!a[OVS_USERSPACE_ATTR_PID] || > - !nla_get_u32(a[OVS_USERSPACE_ATTR_PID])) > - return -EINVAL; > - It can't be removed because it is still required by ovs_dp_upcall(). There is a problem with the action output_userspace which still uses the netlink OVS_USERSPACE_ATTR_PID to set upcall.portid. Later ovs_dp_upcall() returns -ENOTCONN if that is missing. The userspace patchset posted together with this patch does: static uint32_t dpif_netlink_port_get_pid(const struct dpif *dpif_, odp_port_t port_no) { const struct dpif_netlink *dpif = dpif_netlink_cast(dpif_); uint32_t ret; /* In per-cpu dispatch mode, vports do not have an associated PID */ if (DISPATCH_MODE_PER_CPU(dpif)) { return 0; } That is used by compose_slow_path() to create userspace actions. So, it seems all userspace actions would be using id 0 and that would discarded by the kernel with -ENOTCONN. -- fbl _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev
