net: add IFLA_MAX_PACING_OFFLOAD_HORIZON device attribute

Some network devices have the ability to offload EDT (Earliest
Departure Time) which is the model used for TCP pacing and FQ
packet scheduler.

Some of them implement the timing wheel mechanism described in
https://saeed.github.io/files/carousel-sigcomm17.pdf
with an associated 'timing wheel horizon'.

This patch adds dev->max_pacing_offload_horizon expressing
this timing wheel horizon in nsec units.

This is a read-only attribute.

Unless a driver sets it, dev->max_pacing_offload_horizon
is zero.

v2: addressed Jakub feedback ( https://lore.kernel.org/netdev/20240930152304.472767-2-edumazet@google.com/T/#mf6294d714c41cc459962154cc2580ce3c9693663 )
v3: added yaml doc (also per Jakub feedback)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20241003121219.2396589-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

6 files changed, 15 insertions, 0 deletions

diff --git a/Documentation/netlink/specs/rt_link.yaml b/Documentation/netlink/specs/rt_link.yaml
index 0c4d5d40cae9..d7131a1afadf 100644
--- a/Documentation/netlink/specs/rt_link.yaml
+++ b/Documentation/netlink/specs/rt_link.yaml
@@ -1137,6 +1137,10 @@ attribute-sets:
         name: dpll-pin
         type: nest
         nested-attributes: link-dpll-pin-attrs
+      -
+        name: max-pacing-offload-horizon
+        type: uint
+        doc: EDT offload horizon supported by the device (in nsec).
   -
     name: af-spec-attrs
     attributes:
diff --git a/Documentation/networking/net_cachelines/net_device.rst b/Documentation/networking/net_cachelines/net_device.rst
index 22b07c814f4a..49f03cb78c6e 100644
--- a/Documentation/networking/net_cachelines/net_device.rst
+++ b/Documentation/networking/net_cachelines/net_device.rst
@@ -183,3 +183,4 @@ struct_devlink_port*                devlink_port
 struct_dpll_pin*                    dpll_pin                                                        
 struct hlist_head                   page_pools
 struct dim_irq_moder*               irq_moder
+u64                                 max_pacing_offload_horizon
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4d20c776a4ff..49a7e7db0883 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2009,6 +2009,8 @@ enum netdev_reg_state {
  *	@dpll_pin: Pointer to the SyncE source pin of a DPLL subsystem,
  *		   where the clock is recovered.
  *
+ *	@max_pacing_offload_horizon: max EDT offload horizon in nsec.
+ *
  *	FIXME: cleanup struct net_device such that network protocol info
  *	moves out.
  */
@@ -2399,6 +2401,8 @@ struct net_device {
 	/** @irq_moder: dim parameters used if IS_ENABLED(CONFIG_DIMLIB). */
 	struct dim_irq_moder	*irq_moder;
 
+	u64			max_pacing_offload_horizon;
+
 	u8			priv[] ____cacheline_aligned
 				       __counted_by(priv_len);
 } ____cacheline_aligned;
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 6dc258993b17..506ba9c80e83 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -377,6 +377,7 @@ enum {
 	IFLA_GSO_IPV4_MAX_SIZE,
 	IFLA_GRO_IPV4_MAX_SIZE,
 	IFLA_DPLL_PIN,
+	IFLA_MAX_PACING_OFFLOAD_HORIZON,
 	__IFLA_MAX
 };
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index f0a520987085..682d8d3127db 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1118,6 +1118,7 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
 	       + nla_total_size(MAX_ADDR_LEN) /* IFLA_PERM_ADDRESS */
 	       + rtnl_devlink_port_size(dev)
 	       + rtnl_dpll_pin_size(dev)
+	       + nla_total_size(8)  /* IFLA_MAX_PACING_OFFLOAD_HORIZON */
 	       + 0;
 }
 
@@ -1867,6 +1868,8 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
 			READ_ONCE(dev->tso_max_size)) ||
 	    nla_put_u32(skb, IFLA_TSO_MAX_SEGS,
 			READ_ONCE(dev->tso_max_segs)) ||
+	    nla_put_uint(skb, IFLA_MAX_PACING_OFFLOAD_HORIZON,
+			 READ_ONCE(dev->max_pacing_offload_horizon)) ||
 #ifdef CONFIG_RPS
 	    nla_put_u32(skb, IFLA_NUM_RX_QUEUES,
 			READ_ONCE(dev->num_rx_queues)) ||
@@ -1975,6 +1978,7 @@ nla_put_failure:
 }
 
 static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
+	[IFLA_UNSPEC]		= { .strict_start_type = IFLA_DPLL_PIN },
 	[IFLA_IFNAME]		= { .type = NLA_STRING, .len = IFNAMSIZ-1 },
 	[IFLA_ADDRESS]		= { .type = NLA_BINARY, .len = MAX_ADDR_LEN },
 	[IFLA_BROADCAST]	= { .type = NLA_BINARY, .len = MAX_ADDR_LEN },
diff --git a/tools/include/uapi/linux/if_link.h b/tools/include/uapi/linux/if_link.h
index f0d71b2a3f1e..96ec2b01e725 100644
--- a/tools/include/uapi/linux/if_link.h
+++ b/tools/include/uapi/linux/if_link.h
@@ -377,6 +377,7 @@ enum {
 	IFLA_GSO_IPV4_MAX_SIZE,
 	IFLA_GRO_IPV4_MAX_SIZE,
 	IFLA_DPLL_PIN,
+	IFLA_MAX_PACING_OFFLOAD_HORIZON,
 	__IFLA_MAX
 };