Add disk I/O scheduling for positively niced processes.

When a positively niced process requests a disk I/O, make
it wait for its nice value of ticks before scheduling its
I/O request if there are any other processes with I/O
requests in the disk queue. For all the gory details, see
the ``Running fsck in the Background'' paper in the Usenix
BSDCon 2002 Conference Proceedings, pages 55-64.

1 files changed, 25 insertions, 0 deletions

diff --git a/sys/kern/subr_disklabel.c b/sys/kern/subr_disklabel.c
index 1dc0ece..2924c55 100644
--- a/sys/kern/subr_disklabel.c
+++ b/sys/kern/subr_disklabel.c
@@ -44,12 +44,25 @@
 #include <sys/bio.h>
 #include <sys/buf.h>
 #include <sys/conf.h>
+#include <sys/kernel.h>
 #include <sys/disklabel.h>
 #include <sys/diskslice.h>
 #include <sys/syslog.h>
 #include <machine/atomic.h>
 
 /*
+ * Mutex to use when delaying niced I/O bound processes in bioqdisksort().
+ */
+static struct mtx dksort_mtx;
+static void
+dksort_init(void)
+{
+
+	mtx_init(&dksort_mtx, "dksort", MTX_DEF);
+}
+SYSINIT(dksort, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, dksort_init, NULL)
+
+/*
  * Seek sort for disks.
  *
  * The buf_queue keep two queues, sorted in ascending block order.  The first
@@ -72,7 +85,19 @@ bioqdisksort(bioq, bp)
 	struct bio *bq;
 	struct bio *bn;
 	struct bio *be;
+	struct thread *td = curthread;
 	
+	if (td && td->td_ksegrp->kg_nice > 0) {
+		TAILQ_FOREACH(bn, &bioq->queue, bio_queue)
+			if (BIOTOBUF(bn)->b_vp != BIOTOBUF(bn)->b_vp)
+				break;
+		if (bn != NULL) {
+			mtx_lock(&dksort_mtx);
+			msleep((caddr_t)&dksort_mtx, &dksort_mtx,
+			    PPAUSE | PCATCH | PDROP, "ioslow",
+			    td->td_ksegrp->kg_nice);
+		}
+	}
 	if (!atomic_cmpset_int(&bioq->busy, 0, 1))
 		panic("Recursing in bioqdisksort()");
 	be = TAILQ_LAST(&bioq->queue, bio_queue);