When user_frac in the polling subsystem is low it is going to busy the

CPU for too long period than necessary.  Additively, interfaces are kept
polled (in the tick) even if no more packets are available.
In order to avoid such situations a new generic mechanism can be
implemented in proactive way, keeping track of the time spent on any
packet and fragmenting the time for any tick, stopping the processing
as soon as possible.

In order to implement such mechanism, the polling handler needs to
change, returning the number of packets processed.
While the intended logic is not part of this patch, the polling KPI is
broken by this commit, adding an int return value and the new flag
IFCAP_POLLING_NOCOUNT (which will signal that the return value is
meaningless for the installed handler and checking should be skipped).

Bump __FreeBSD_version in order to signal such situation.

Reviewed by:	emaste
Sponsored by:	Sandvine Incorporated

1 files changed, 14 insertions, 8 deletions

diff --git a/sys/dev/ixgb/if_ixgb.c b/sys/dev/ixgb/if_ixgb.c
index 1fb3544..f555e79 100644
--- a/sys/dev/ixgb/if_ixgb.c
+++ b/sys/dev/ixgb/if_ixgb.c
@@ -121,7 +121,7 @@ static void     ixgb_update_stats_counters(struct adapter *);
 static void     ixgb_clean_transmit_interrupts(struct adapter *);
 static int      ixgb_allocate_receive_structures(struct adapter *);
 static int      ixgb_allocate_transmit_structures(struct adapter *);
-static void     ixgb_process_receive_interrupts(struct adapter *, int);
+static int      ixgb_process_receive_interrupts(struct adapter *, int);
 static void 
 ixgb_receive_checksum(struct adapter *,
 		      struct ixgb_rx_desc * rx_desc,
@@ -748,11 +748,12 @@ ixgb_init(void *arg)
 }
 
 #ifdef DEVICE_POLLING
-static void
+static int
 ixgb_poll_locked(struct ifnet * ifp, enum poll_cmd cmd, int count)
 {
 	struct adapter *adapter = ifp->if_softc;
 	u_int32_t       reg_icr;
+	int		rx_npkts;
 
 	IXGB_LOCK_ASSERT(adapter);
 
@@ -766,22 +767,25 @@ ixgb_poll_locked(struct ifnet * ifp, enum poll_cmd cmd, int count)
 			    adapter);
 		}
 	}
-	ixgb_process_receive_interrupts(adapter, count);
+	rx_npkts = ixgb_process_receive_interrupts(adapter, count);
 	ixgb_clean_transmit_interrupts(adapter);
 
 	if (ifp->if_snd.ifq_head != NULL)
 		ixgb_start_locked(ifp);
+	return (rx_npkts);
 }
 
-static void
+static int
 ixgb_poll(struct ifnet * ifp, enum poll_cmd cmd, int count)
 {
 	struct adapter *adapter = ifp->if_softc;
+	int rx_npkts = 0;
 
 	IXGB_LOCK(adapter);
 	if (ifp->if_drv_flags & IFF_DRV_RUNNING)
-		ixgb_poll_locked(ifp, cmd, count);
+		rx_npkts = ixgb_poll_locked(ifp, cmd, count);
 	IXGB_UNLOCK(adapter);
+	return (rx_npkts);
 }
 #endif /* DEVICE_POLLING */
 
@@ -2065,7 +2069,7 @@ ixgb_free_receive_structures(struct adapter * adapter)
  *  count < 0.
  *
  *********************************************************************/
-static void
+static int
 ixgb_process_receive_interrupts(struct adapter * adapter, int count)
 {
 	struct ifnet   *ifp;
@@ -2079,6 +2083,7 @@ ixgb_process_receive_interrupts(struct adapter * adapter, int count)
 	int             i;
 	int             next_to_use = 0;
 	int             eop_desc;
+	int		rx_npkts = 0;
 	/* Pointer to the receive descriptor being examined. */
 	struct ixgb_rx_desc *current_desc;
 
@@ -2094,7 +2099,7 @@ ixgb_process_receive_interrupts(struct adapter * adapter, int count)
 #ifdef _SV_
 		adapter->no_pkts_avail++;
 #endif
-		return;
+		return (rx_npkts);
 	}
 	while ((current_desc->status & IXGB_RX_DESC_STATUS_DD) && (count != 0)) {
 
@@ -2168,6 +2173,7 @@ ixgb_process_receive_interrupts(struct adapter * adapter, int count)
 					IXGB_UNLOCK(adapter);
 					(*ifp->if_input) (ifp, adapter->fmp);
 					IXGB_LOCK(adapter);
+					rx_npkts++;
 				}
 #endif
 				adapter->fmp = NULL;
@@ -2239,7 +2245,7 @@ ixgb_process_receive_interrupts(struct adapter * adapter, int count)
 	/* Advance the IXGB's Receive Queue #0  "Tail Pointer" */
 	IXGB_WRITE_REG(&adapter->hw, RDT, next_to_use);
 
-	return;
+	return (rx_npkts);
 }
 
 /*********************************************************************