[src/trunk]: src/sys/dev/ic Rework the command queue, to avoid having command...

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

details:   https://anonhg.NetBSD.org/src/rev/dab5b0c798e6
branches:  trunk
changeset: 485772:dab5b0c798e6
user:      bouyer <bouyer%NetBSD.org@localhost>
date:      Fri May 05 09:05:44 2000 +0000

description:
Rework the command queue, to avoid having commands blocked at the end
of the queue. Load is now properly balanced across all disks of the same bus.

diffstat:

 sys/dev/ic/siop.c |  47 ++++++++++++++++++++++++++++-------------------
 1 files changed, 28 insertions(+), 19 deletions(-)

diffs (85 lines):

diff -r 0cb1b96b236e -r dab5b0c798e6 sys/dev/ic/siop.c
--- a/sys/dev/ic/siop.c Fri May 05 08:03:12 2000 +0000
+++ b/sys/dev/ic/siop.c Fri May 05 09:05:44 2000 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: siop.c,v 1.9 2000/05/04 17:18:27 bouyer Exp $  */
+/*     $NetBSD: siop.c,v 1.10 2000/05/05 09:05:44 bouyer Exp $ */
 
 /*
  * Copyright (c) 2000 Manuel Bouyer.
@@ -1587,7 +1587,7 @@
        u_int32_t *scr;
        u_int32_t dsa;
        int timeout;
-       int target, lun, slot, maxslot, maxslot0;
+       int target, lun, slot;
        int newcmd = 0; 
 
        /*
@@ -1596,15 +1596,30 @@
        siop_script_sync(sc, BUS_DMASYNC_POSTREAD | BUS_DMASYNC_POSTWRITE);
 
        /*
-        * we need to treat the slots as circular queue (to give a chance
-        * to others commands to execute). So we have to remember the
-        * last used slot in sc_currshedslot.
+        * The queue management here is a bit tricky: the script always looks
+        * at the slot from first to last, so if we always use the first 
+        * free slot commands can stay at the tail of the queue ~forever.
+        * The algorithm used here is to restart from the head when we know
+        * that the queue is empty, and only add commands after the last one.
+        * When we're at the end of the queue wait for the script to clear it.
+        * The best thing to do here would be to implement a circular queue,
+        * but using only 53c720 features this can be "interesting".
+        * A mid-way solution could be to implement 2 queues and swap orders.
         */
-       maxslot0 = sc->sc_currshedslot + 1;
-       maxslot = sc->sc_nshedslots;
-       slot = sc->sc_currshedslot + 1;
-       if (slot >= sc->sc_nshedslots)
-               sc->sc_currshedslot = slot = 0;
+       slot = sc->sc_currshedslot;
+       scr = &sc->sc_script[Ent_sheduler / 4 +
+           (Ent_nextslot / 4) * slot];
+       /*
+        * if relative addr of first jump is not 0 the slot is free. As this is 
+        * the last used slot, all previous slots are free, we can restart
+        * from 0.
+        */
+       if (scr[Ent_slot / 4 + 1] != 0) {
+               slot = sc->sc_currshedslot = 0;
+       } else {
+               slot++;
+       }
+       
        for (target = 0; target <= sc->sc_link.scsipi_scsi.max_target;
            target++) {
                if (sc->targets[target] == NULL)
@@ -1618,8 +1633,7 @@
                            siop_cmd->status != CMDST_SENSE)
                                continue;
                        /* find a free sheduler slot and load it */
-retry:
-                       for (; slot < maxslot; slot++) {
+                       for (; slot < sc->sc_nshedslots; slot++) {
                                scr = &sc->sc_script[Ent_sheduler / 4 +
                                    (Ent_nextslot / 4) * slot];
                                /*
@@ -1682,15 +1696,10 @@
                                scr[Ent_slot / 4 + 1] = 0;
                                break;
                        }
-                       /* if we reached the end, restart at the beggining */
+                       /* no more free slot, no need to continue */
                        if (slot == sc->sc_nshedslots) {
-                               slot = 0;
-                               maxslot = maxslot0;
-                               goto retry;
+                               goto end;
                        }
-                       /* no more free slot, no need to continue */
-                       if (slot == sc->sc_currshedslot)
-                               goto end;
                        sc->sc_currshedslot = slot;
                }
        }