@@ -3389,6 +3389,24 @@ netif_xmit_frozen_or_drv_stopped(const struct netdev_queue *dev_queue)
return dev_queue->state & QUEUE_STATE_DRV_XOFF_OR_FROZEN;
}
+/**
+ * netdev_queue_set_dql_min_limit - set dql minimum limit
+ * @dev_queue: pointer to transmit queue
+ * @min_limit: dql minimum limit
+ *
+ * Forces xmit_more() to return true until the minimum threshold
+ * defined by @min_limit is reached (or until the tx queue is
+ * empty). Warning: to be use with care, misuse will impact the
+ * latency.
+ */
+static inline void netdev_queue_set_dql_min_limit(struct netdev_queue *dev_queue,
+ unsigned int min_limit)
+{
+#ifdef CONFIG_BQL
+ dev_queue->dql.min_limit = min_limit;
+#endif
+}
+
/**
* netdev_txq_bql_enqueue_prefetchw - prefetch bql data for write
* @dev_queue: pointer to transmit queue
Add a function to set the dynamic queue limit minimum value. Some specific drivers might have legitimate reasons to configure dql.min_limit to a given value. Typically, this is the case when the PDU of the protocol is smaller than the packet size to used to carry those frames to the device. Concrete example: a CAN (Control Area Network) device with an USB 2.0 interface. The PDU of classical CAN protocol are roughly 16 bytes but the USB packet size (which is used to carry the CAN frames to the device) might be up to 512 bytes. Wen small traffic burst occurs, BQL algorithm is not able to immediately adjust and this would result in having to send many small USB packets (i.e packet of 16 bytes for each CAN frame). Filling up the USB packet with CAN frames is relatively fast (small latency issue) but the gain of not having to send several small USB packets is huge (big throughput increase). In this case, forcing dql.min_limit to a given value that would allow to stuff the USB packet is always a win. This function is to be used by network drivers which are able to prove through a rationale and through empirical tests on several environment (with other applications, heavy context switching, virtualization...), that they constantly reach better performances with a specific predefined dql.min_limit value with no noticeable latency impact. Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> --- include/linux/netdevice.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)