[src/trunk]: src/sys/dev revert 1.90 of dksubr.c and change sc_deferred back ...

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

details:   https://anonhg.NetBSD.org/src/rev/2cadc8ab9466
branches:  trunk
changeset: 348545:2cadc8ab9466
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Mon Oct 24 17:14:27 2016 +0000

description:
revert 1.90 of dksubr.c and change sc_deferred back to simple pointer; the
global sc_busy flag guards against race so it's not actually necessary, and
this place is unlikely to need to be parallelized in near future

discussed with mlelstv@

diffstat:

 sys/dev/dksubr.c |  33 ++++++++++++++++-----------------
 sys/dev/dkvar.h  |   4 ++--
 2 files changed, 18 insertions(+), 19 deletions(-)

diffs (103 lines):

diff -r e0c07486d853 -r 2cadc8ab9466 sys/dev/dksubr.c
--- a/sys/dev/dksubr.c  Mon Oct 24 06:04:26 2016 +0000
+++ b/sys/dev/dksubr.c  Mon Oct 24 17:14:27 2016 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: dksubr.c,v 1.90 2016/10/22 22:32:33 jdolecek Exp $ */
+/* $NetBSD: dksubr.c,v 1.91 2016/10/24 17:14:27 jdolecek Exp $ */
 
 /*-
  * Copyright (c) 1996, 1997, 1998, 1999, 2002, 2008 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: dksubr.c,v 1.90 2016/10/22 22:32:33 jdolecek Exp $");
+__KERNEL_RCSID(0, "$NetBSD: dksubr.c,v 1.91 2016/10/24 17:14:27 jdolecek Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -105,8 +105,6 @@
        /* Attach the device into the rnd source list. */
        rnd_attach_source(&dksc->sc_rnd_source, dksc->sc_xname,
            RND_TYPE_DISK, RND_FLAG_DEFAULT);
-
-       TAILQ_INIT(&dksc->sc_deferred);
 }
 
 void
@@ -380,27 +378,25 @@
         *
         * So when a diskstart fails, the buffer is saved
         * and tried again before the next buffer is fetched.
-        * dk_drain() handles flushing of a saved buffer(s).
+        * dk_drain() handles flushing of a saved buffer.
         *
         * This keeps order of I/O operations, unlike bufq_put.
         */
 
-       for(;;) {
-               bp = TAILQ_FIRST(&dksc->sc_deferred);
-               if (__predict_false(bp != NULL))
-                       TAILQ_REMOVE(&dksc->sc_deferred, bp, b_actq);
-               else {
-                       bp = bufq_get(dksc->sc_bufq);
-                       if (bp == NULL)
-                               break;
-               }
+       bp = dksc->sc_deferred;
+       dksc->sc_deferred = NULL;
+
+       if (bp == NULL)
+               bp = bufq_get(dksc->sc_bufq);
+
+       while (bp != NULL) {
 
                disk_busy(&dksc->sc_dkdev);
                mutex_exit(&dksc->sc_iolock);
                error = dkd->d_diskstart(dksc->sc_dev, bp);
                mutex_enter(&dksc->sc_iolock);
                if (error == EAGAIN) {
-                       TAILQ_INSERT_TAIL(&dksc->sc_deferred, bp, b_actq);
+                       dksc->sc_deferred = bp;
                        disk_unbusy(&dksc->sc_dkdev, 0, (bp->b_flags & B_READ));
                        break;
                }
@@ -410,6 +406,8 @@
                        bp->b_resid = bp->b_bcount;
                        dk_done1(dksc, bp, false);
                }
+
+               bp = bufq_get(dksc->sc_bufq);
        }
 
        dksc->sc_busy = false;
@@ -453,8 +451,9 @@
        struct buf *bp;
 
        mutex_enter(&dksc->sc_iolock);
-       while ((bp = TAILQ_FIRST(&dksc->sc_deferred)) != NULL) {
-               TAILQ_REMOVE(&dksc->sc_deferred, bp, b_actq);
+       bp = dksc->sc_deferred;
+       dksc->sc_deferred = NULL;
+       if (bp != NULL) {
                bp->b_error = EIO;
                bp->b_resid = bp->b_bcount;
                biodone(bp); 
diff -r e0c07486d853 -r 2cadc8ab9466 sys/dev/dkvar.h
--- a/sys/dev/dkvar.h   Mon Oct 24 06:04:26 2016 +0000
+++ b/sys/dev/dkvar.h   Mon Oct 24 17:14:27 2016 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: dkvar.h,v 1.26 2016/10/22 22:32:33 jdolecek Exp $ */
+/* $NetBSD: dkvar.h,v 1.27 2016/10/24 17:14:27 jdolecek Exp $ */
 
 /*-
  * Copyright (c) 2002 The NetBSD Foundation, Inc.
@@ -49,7 +49,7 @@
        kmutex_t                 sc_iolock;     /* protects buffer queue */
        struct bufq_state       *sc_bufq;       /* buffer queue */
        int                      sc_dtype;      /* disk type */
-       TAILQ_HEAD(, buf)        sc_deferred;   /* retry after start failed */
+       struct buf              *sc_deferred;   /* retry after start failed */
        bool                     sc_busy;       /* processing buffers */
        krndsource_t             sc_rnd_source; /* entropy source */
 };