[src/trunk]: src/sys/arch/xen/xen Stop using IFF_OACTIVE, just keep processin...

[jdolecek <jdolecek%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/0aa5f13f8f8d
branches:  trunk
changeset: 970519:0aa5f13f8f8d
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Thu Mar 26 18:32:21 2020 +0000

description:
Stop using IFF_OACTIVE, just keep processing until we fill the Tx ring

xennet_tx_complete() is now called only in xennet_softstart() just
before processing Tx queue; xennet_handler() just schedules the
softint for xennet_softstart() iff the Tx ring list is completely empty

no performance changes observed

XXX the detach and suspend code expects xennet_handler() to collect
XXX the Tx responses, the tsleep() loop should still work since the tsleep()
XXX would allow the softint to trigger; untested though

diffstat:

 sys/arch/xen/xen/if_xennet_xenbus.c |  48 +++++++++++++-----------------------
 1 files changed, 17 insertions(+), 31 deletions(-)

diffs (147 lines):

diff -r 2e4af1bfe3db -r 0aa5f13f8f8d sys/arch/xen/xen/if_xennet_xenbus.c
--- a/sys/arch/xen/xen/if_xennet_xenbus.c       Thu Mar 26 18:28:09 2020 +0000
+++ b/sys/arch/xen/xen/if_xennet_xenbus.c       Thu Mar 26 18:32:21 2020 +0000
@@ -1,4 +1,4 @@
-/*      $NetBSD: if_xennet_xenbus.c,v 1.94 2020/03/22 11:20:59 jdolecek Exp $      */
+/*      $NetBSD: if_xennet_xenbus.c,v 1.95 2020/03/26 18:32:21 jdolecek Exp $      */
 
 /*
  * Copyright (c) 2006 Manuel Bouyer.
@@ -64,11 +64,8 @@
  * xennet_start() (default output routine of xennet) that schedules a softint,
  * xennet_softstart(). xennet_softstart() generates the requests associated
  * to the TX mbufs queued (see altq(9)).
- * The backend's responses are processed by xennet_tx_complete(), called either
- * from:
- * - xennet_start()
- * - xennet_handler(), during an asynchronous event notification from backend
- *   (similar to an IRQ).
+ * The backend's responses are processed by xennet_tx_complete(), called
+ * from xennet_softstart()
  *
  * for RX:
  * Purpose is to process the packets received from the outside. RX buffers
@@ -84,7 +81,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_xennet_xenbus.c,v 1.94 2020/03/22 11:20:59 jdolecek Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_xennet_xenbus.c,v 1.95 2020/03/26 18:32:21 jdolecek Exp $");
 
 #include "opt_xen.h"
 #include "opt_nfs_boot.h"
@@ -934,7 +931,7 @@
 /*
  * Process responses associated to the TX mbufs sent previously through
  * xennet_softstart()
- * Called at splnet.
+ * Called at splsoftnet.
  */
 static void
 xennet_tx_complete(struct xennet_xenbus_softc *sc)
@@ -958,7 +955,7 @@
                        aprint_verbose_dev(sc->sc_dev,
                            "grant still used by backend\n");
                        sc->sc_tx_ring.rsp_cons = i;
-                       goto end;
+                       return;
                }
                if (__predict_false(
                    RING_GET_RESPONSE(&sc->sc_tx_ring, i)->status !=
@@ -980,11 +977,6 @@
        xen_wmb();
        if (resp_prod != sc->sc_tx_ring.sring->rsp_prod)
                goto again;
-end:
-       if (ifp->if_flags & IFF_OACTIVE) {
-               ifp->if_flags &= ~IFF_OACTIVE;
-               softint_schedule(sc->sc_softintr);
-       }
 }
 
 /*
@@ -1011,7 +1003,11 @@
        if (sc->sc_backend_status != BEST_CONNECTED)
                return 1;
 
-       xennet_tx_complete(sc);
+       /* Poke Tx queue if we run out of Tx buffers earlier */
+       mutex_enter(&sc->sc_tx_lock);
+       if (SLIST_EMPTY(&sc->sc_txreq_head))
+               softint_schedule(sc->sc_softintr);
+       mutex_exit(&sc->sc_tx_lock);
 
        rnd_add_uint32(&sc->sc_rnd_source, sc->sc_tx_ring.req_prod_pvt);
 
@@ -1162,12 +1158,6 @@
 
        rnd_add_uint32(&sc->sc_rnd_source, sc->sc_tx_ring.req_prod_pvt);
 
-       xennet_tx_complete(sc);
-
-       if (__predict_false(
-           (ifp->if_flags & (IFF_RUNNING | IFF_OACTIVE)) != IFF_RUNNING))
-               return;
-
        /*
         * The Xen communication channel is much more efficient if we can
         * schedule batch of packets for domain0. To achieve this, we
@@ -1196,12 +1186,12 @@
        int notify;
        int do_notify = 0;
 
+       if ((ifp->if_flags & IFF_RUNNING) == 0)
+               return;
+
+       xennet_tx_complete(sc);
+
        mutex_enter(&sc->sc_tx_lock);
-       if (__predict_false(
-           (ifp->if_flags & (IFF_RUNNING | IFF_OACTIVE)) != IFF_RUNNING)) {
-               mutex_exit(&sc->sc_tx_lock);
-               return;
-       }
 
        req_prod = sc->sc_tx_ring.req_prod_pvt;
        while (/*CONSTCOND*/1) {
@@ -1209,7 +1199,6 @@
 
                req = SLIST_FIRST(&sc->sc_txreq_head);
                if (__predict_false(req == NULL)) {
-                       ifp->if_flags |= IFF_OACTIVE;
                        break;
                }
                IFQ_POLL(&ifp->if_snd, m);
@@ -1280,7 +1269,6 @@
                            xpmap_ptom_masked(pa),
                            GNTMAP_readonly, &req->txreq_gntref) != 0)) {
                                m_freem(new_m);
-                               ifp->if_flags |= IFF_OACTIVE;
                                break;
                        }
                        /* we will be able to send new_m */
@@ -1292,7 +1280,6 @@
                            sc->sc_xbusd->xbusd_otherend_id,
                            xpmap_ptom_masked(pa),
                            GNTMAP_readonly, &req->txreq_gntref) != 0)) {
-                               ifp->if_flags |= IFF_OACTIVE;
                                break;
                        }
                        /* we will be able to send m */
@@ -1409,7 +1396,6 @@
                xennet_reset(sc);
        }
        ifp->if_flags |= IFF_RUNNING;
-       ifp->if_flags &= ~IFF_OACTIVE;
        ifp->if_timer = 0;
        mutex_exit(&sc->sc_rx_lock);
        return 0;
@@ -1420,7 +1406,7 @@
 {
        struct xennet_xenbus_softc *sc = ifp->if_softc;
 
-       ifp->if_flags &= ~(IFF_RUNNING | IFF_OACTIVE);
+       ifp->if_flags &= ~IFF_RUNNING;
        hypervisor_mask_event(sc->sc_evtchn);
        xennet_reset(sc);
 }