[src/trunk]: src/sys/dev/ic Calling DELAY() during polling for command comple...

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

details:   https://anonhg.NetBSD.org/src/rev/e057a06549bb
branches:  trunk
changeset: 472062:e057a06549bb
user:      jonathan <jonathan%NetBSD.org@localhost>
date:      Tue Apr 20 04:40:24 1999 +0000

description:
Calling DELAY() during polling for command completion of the normal
per-packet discard of every received packet increases latency and
decrease throughput.  INstead, Spin on S_COMMAND_IN_PROGESS for enough
iterations as the expected time to completion.  Only do DELAY()/poll
loops (as suggested by Jason Thorpe) if spinning fails.
Take PCI as fastest case and compute worst-case estimate.

Shorten DELAY() in S_COMMAND_COMPLETE polling-loop up 10, loop-count
down.  to speed up epreset() completion (m/c filter change, ifup/ipdown, etc).

diffstat:

 sys/dev/ic/elink3.c |  27 ++++++++++++++++++++-------
 1 files changed, 20 insertions(+), 7 deletions(-)

diffs (58 lines):

diff -r 9a75d0676cee -r e057a06549bb sys/dev/ic/elink3.c
--- a/sys/dev/ic/elink3.c       Tue Apr 20 00:45:24 1999 +0000
+++ b/sys/dev/ic/elink3.c       Tue Apr 20 04:40:24 1999 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: elink3.c,v 1.56 1999/04/19 23:26:48 jonathan Exp $     */
+/*     $NetBSD: elink3.c,v 1.57 1999/04/20 04:40:24 jonathan Exp $     */
 
 /*-
  * Copyright (c) 1998 The NetBSD Foundation, Inc.
@@ -277,12 +277,12 @@
        bus_space_handle_t ioh;
 
 {
-       register int i;
+       int i;
 
-       for (i = 0; i < 1000; i++) {
-       if (bus_space_read_2(iot, ioh, ELINK_STATUS) & S_COMMAND_IN_PROGRESS)
-               return;
-       DELAY(100);
+       for (i = 0; i < 10000; i++) {
+               if ((bus_space_read_2(iot, ioh, ELINK_STATUS) & S_COMMAND_IN_PROGRESS) == 0)
+                       break;
+               DELAY(10);
        }
 }
 
@@ -299,7 +299,6 @@
        register bus_space_handle_t ioh = sc->sc_ioh;
 
        bus_space_write_2(iot, ioh, cmd, arg);
-
        ep_finish_reset(iot, ioh);
 }
 
@@ -309,8 +308,22 @@
        register bus_space_tag_t iot;
        register bus_space_handle_t ioh;
 {
+       int i;
 
        bus_space_write_2(iot, ioh, ELINK_COMMAND, RX_DISCARD_TOP_PACK);
+
+        /*
+        * Spin for about 1 msec, to avoid forcing a DELAY() between
+        * every received packet (adding latency and  limiting pkt-recv rate).
+        * On PCI, at 4 30-nsec PCI bus cycles for a read, 8000 iterations
+        * is about right.
+        */
+       for (i = 0; i < 8000; i++) {
+               if  ((bus_space_read_2(iot, ioh, ELINK_STATUS) & S_COMMAND_IN_PROGRESS) == 0)
+                   return;
+       }
+
+       /*  Didn't complete in a hurry. Do DELAY()s. */
        ep_finish_reset(iot, ioh);
 }