ibmveth: Optimize poll rescheduling process

JIRA: https://issues.redhat.com/browse/RHEL-52913

commit f128c7c
Author: Nick Child <nnac123@linux.ibm.com>
Date:   Thu Aug 1 16:12:14 2024 -0500

    ibmveth: Optimize poll rescheduling process

    When the ibmveth driver processes less than the budget, it must call
    napi_complete_done() to release the instance. This function will
    return false if the driver should avoid rearming interrupts.
    Previously, the driver was ignoring the return code of
    napi_complete_done(). As a result, there were unnecessary calls to
    enable the veth irq.
    Therefore, use the return code napi_complete_done() to determine if
    irq rearm is necessary.

    Additionally, in the event that new data is received immediately after
    rearming interrupts, rather than just rescheduling napi, also jump
    back to the poll processing loop since we are already in the poll
    function (and know that we did not expense all of budget).

    This slight tweak results in a 15% increase in TCP_RR transaction rate
    (320k to 370k txns). We can see the ftrace data supports this:
    PREV: ibmveth_poll = 8818014.0 us / 182802.0 hits = AVG 48.24
    NEW:  ibmveth_poll = 8082398.0 us / 191413.0 hits = AVG 42.22

    Signed-off-by: Nick Child <nnac123@linux.ibm.com>
    Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
    Link: https://patch.msgid.link/20240801211215.128101-2-nnac123@linux.ibm.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

drivers/net/ethernet/ibm/ibmveth.c

@@ -1342,6 +1342,7 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
 	unsigned long lpar_rc;
 	u16 mss = 0;
 
+restart_poll:
 	while (frames_processed < budget) {
 		if (!ibmveth_rxq_pending_buffer(adapter))
 			break;
@@ -1425,24 +1426,25 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
 
 	ibmveth_replenish_task(adapter);
 
-	if (frames_processed < budget) {
-		napi_complete_done(napi, frames_processed);
+	if (frames_processed == budget)
+		goto out;
 
-		/* We think we are done - reenable interrupts,
-		 * then check once more to make sure we are done.
-		 */
-		lpar_rc = h_vio_signal(adapter->vdev->unit_address,
-				       VIO_IRQ_ENABLE);
+	if (!napi_complete_done(napi, frames_processed))
+		goto out;
 
-		BUG_ON(lpar_rc != H_SUCCESS);
+	/* We think we are done - reenable interrupts,
+	 * then check once more to make sure we are done.
+	 */
+	lpar_rc = h_vio_signal(adapter->vdev->unit_address, VIO_IRQ_ENABLE);
+	BUG_ON(lpar_rc != H_SUCCESS);
 
-		if (ibmveth_rxq_pending_buffer(adapter) &&
-		    napi_schedule(napi)) {
-			lpar_rc = h_vio_signal(adapter->vdev->unit_address,
-					       VIO_IRQ_DISABLE);
-		}
+	if (ibmveth_rxq_pending_buffer(adapter) && napi_schedule(napi)) {
+		lpar_rc = h_vio_signal(adapter->vdev->unit_address,
+				       VIO_IRQ_DISABLE);
+		goto restart_poll;
 	}
 
+out:
 	return frames_processed;
 }