Module Name: src
Committed By: yamt
Date: Wed Nov 2 15:14:49 UTC 2011
Modified Files:
src/sys/kern: bufq_priocscan.c
Log Message:
- don't forget to decrement burst count after reset
- signed -> unsigned where appropriate
- comments
To generate a diff of this commit:
cvs rdiff -u -r1.14 -r1.15 src/sys/kern/bufq_priocscan.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/bufq_priocscan.c
diff -u src/sys/kern/bufq_priocscan.c:1.14 src/sys/kern/bufq_priocscan.c:1.15
--- src/sys/kern/bufq_priocscan.c:1.14 Mon Jan 19 14:54:28 2009
+++ src/sys/kern/bufq_priocscan.c Wed Nov 2 15:14:49 2011
@@ -1,4 +1,4 @@
-/* $NetBSD: bufq_priocscan.c,v 1.14 2009/01/19 14:54:28 yamt Exp $ */
+/* $NetBSD: bufq_priocscan.c,v 1.15 2011/11/02 15:14:49 yamt Exp $ */
/*-
* Copyright (c)2004,2005,2006,2008,2009 YAMAMOTO Takashi,
@@ -27,7 +27,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: bufq_priocscan.c,v 1.14 2009/01/19 14:54:28 yamt Exp $");
+__KERNEL_RCSID(0, "$NetBSD: bufq_priocscan.c,v 1.15 2011/11/02 15:14:49 yamt Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@@ -42,7 +42,7 @@ __KERNEL_RCSID(0, "$NetBSD: bufq_priocsc
TAILQ_HEAD(bqhead, buf);
struct cscan_queue {
struct bqhead cq_head[2]; /* actual lists of buffers */
- int cq_idx; /* current list index */
+ unsigned int cq_idx; /* current list index */
int cq_lastcylinder; /* b_cylinder of the last request */
daddr_t cq_lastrawblkno; /* b_rawblkno of the last request */
};
@@ -65,7 +65,7 @@ cscan_put(struct cscan_queue *q, struct
struct buf tmp;
struct buf *it;
struct bqhead *bqh;
- int idx;
+ unsigned int idx;
tmp.b_cylinder = q->cq_lastcylinder;
tmp.b_rawblkno = q->cq_lastrawblkno;
@@ -90,7 +90,7 @@ cscan_put(struct cscan_queue *q, struct
static struct buf *
cscan_get(struct cscan_queue *q, int remove)
{
- int idx = q->cq_idx;
+ unsigned int idx = q->cq_idx;
struct bqhead *bqh;
struct buf *bp;
@@ -138,7 +138,7 @@ cscan_init(struct cscan_queue *q)
struct priocscan_queue {
struct cscan_queue q_queue;
- int q_burst;
+ unsigned int q_burst;
};
struct bufq_priocscan {
@@ -204,77 +204,108 @@ bufq_priocscan_get(struct bufq_state *bu
{
struct bufq_priocscan *q = bufq->bq_private;
struct priocscan_queue *pq, *npq;
- struct priocscan_queue *first; /* first non-empty queue */
+ struct priocscan_queue *first; /* highest priority non-empty queue */
const struct priocscan_queue *epq;
- const struct cscan_queue *cq;
struct buf *bp;
bool single; /* true if there's only one non-empty queue */
+ /*
+ * find the highest priority non-empty queue.
+ */
pq = &q->bq_queue[0];
epq = pq + PRIOCSCAN_NQUEUE;
for (; pq < epq; pq++) {
- cq = &pq->q_queue;
- if (!cscan_empty(cq))
+ if (!cscan_empty(&pq->q_queue)) {
break;
+ }
}
if (pq == epq) {
- /* there's no requests */
+ /*
+ * all our queues are empty. there's nothing to serve.
+ */
return NULL;
}
-
first = pq;
+
+ /*
+ * scan the rest of queues.
+ *
+ * if we have two or more non-empty queues, we serve the highest
+ * priority one with non-zero burst count.
+ */
single = true;
- for (npq = first + 1; npq < epq; npq++) {
- cq = &npq->q_queue;
- if (!cscan_empty(cq)) {
+ for (npq = pq + 1; npq < epq; npq++) {
+ if (!cscan_empty(&npq->q_queue)) {
+ /*
+ * we found another non-empty queue.
+ * it means that a queue needs to consume its burst
+ * count to be served.
+ */
single = false;
- if (pq->q_burst > 0)
+
+ /*
+ * check if our current candidate queue has already
+ * exhausted its burst count.
+ */
+ if (pq->q_burst > 0) {
break;
+ }
pq = npq;
}
}
if (single) {
/*
- * there's only a non-empty queue. just serve it.
- */
- pq = first;
- } else if (pq->q_burst > 0) {
- /*
- * XXX account only by number of requests. is it good enough?
+ * there's only a non-empty queue.
+ * just serve it without consuming its burst count.
*/
- if (remove) {
- pq->q_burst--;
- }
+ KASSERT(pq == first);
} else {
/*
- * no queue was selected due to burst counts
+ * there are two or more non-empty queues.
*/
- int i;
+ if (pq->q_burst == 0) {
+ /*
+ * no queues can be served because they have already
+ * exhausted their burst count.
+ */
+ unsigned int i;
#ifdef DEBUG
- for (i = 0; i < PRIOCSCAN_NQUEUE; i++) {
- pq = &q->bq_queue[i];
- cq = &pq->q_queue;
- if (!cscan_empty(cq) && pq->q_burst)
- panic("%s: inconsist", __func__);
- }
-#endif /* DEBUG */
-
- /*
- * reset burst counts
- */
- if (remove) {
for (i = 0; i < PRIOCSCAN_NQUEUE; i++) {
pq = &q->bq_queue[i];
- pq->q_burst = priocscan_burst[i];
+ if (!cscan_empty(&pq->q_queue) && pq->q_burst) {
+ panic("%s: inconsist", __func__);
+ }
+ }
+#endif /* DEBUG */
+ /*
+ * reset burst counts.
+ */
+ if (remove) {
+ for (i = 0; i < PRIOCSCAN_NQUEUE; i++) {
+ pq = &q->bq_queue[i];
+ pq->q_burst = priocscan_burst[i];
+ }
}
- }
+ /*
+ * serve the highest priority non-empty queue.
+ */
+ pq = first;
+ }
/*
- * serve first non-empty queue.
+ * consume the burst count.
+ *
+ * XXX account only by number of requests. is it good enough?
*/
- pq = first;
+ KASSERT(pq->q_burst > 0);
+ if (remove) {
+ pq->q_burst--;
+ }
}
+ /*
+ * finally, get a request from the selected queue.
+ */
KDASSERT(!cscan_empty(&pq->q_queue));
bp = cscan_get(&pq->q_queue, remove);
KDASSERT(bp != NULL);
@@ -287,7 +318,7 @@ static struct buf *
bufq_priocscan_cancel(struct bufq_state *bufq, struct buf *bp)
{
struct bufq_priocscan * const q = bufq->bq_private;
- int i, j;
+ unsigned int i, j;
for (i = 0; i < PRIOCSCAN_NQUEUE; i++) {
struct cscan_queue * const cq = &q->bq_queue[i].q_queue;
@@ -318,7 +349,7 @@ static void
bufq_priocscan_init(struct bufq_state *bufq)
{
struct bufq_priocscan *q;
- int i;
+ unsigned int i;
bufq->bq_get = bufq_priocscan_get;
bufq->bq_put = bufq_priocscan_put;
