[PATCH] Improve CD/DVD packet driver write performance
This patch improves write performance for the CD/DVD packet writing driver.
The logic for switching between reading and writing has been changed so
that streaming writes are no longer interrupted by read requests.
Signed-off-by: Peter Osterlund <petero2@telia.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index bc56770..7f3d78d 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -467,14 +467,12 @@
* Queue a bio for processing by the low-level CD device. Must be called
* from process context.
*/
-static void pkt_queue_bio(struct pktcdvd_device *pd, struct bio *bio, int high_prio_read)
+static void pkt_queue_bio(struct pktcdvd_device *pd, struct bio *bio)
{
spin_lock(&pd->iosched.lock);
if (bio_data_dir(bio) == READ) {
pkt_add_list_last(bio, &pd->iosched.read_queue,
&pd->iosched.read_queue_tail);
- if (high_prio_read)
- pd->iosched.high_prio_read = 1;
} else {
pkt_add_list_last(bio, &pd->iosched.write_queue,
&pd->iosched.write_queue_tail);
@@ -490,15 +488,16 @@
* requirements for CDRW drives:
* - A cache flush command must be inserted before a read request if the
* previous request was a write.
- * - Switching between reading and writing is slow, so don't it more often
+ * - Switching between reading and writing is slow, so don't do it more often
* than necessary.
+ * - Optimize for throughput at the expense of latency. This means that streaming
+ * writes will never be interrupted by a read, but if the drive has to seek
+ * before the next write, switch to reading instead if there are any pending
+ * read requests.
* - Set the read speed according to current usage pattern. When only reading
* from the device, it's best to use the highest possible read speed, but
* when switching often between reading and writing, it's better to have the
* same read and write speeds.
- * - Reads originating from user space should have higher priority than reads
- * originating from pkt_gather_data, because some process is usually waiting
- * on reads of the first kind.
*/
static void pkt_iosched_process_queue(struct pktcdvd_device *pd)
{
@@ -512,21 +511,24 @@
for (;;) {
struct bio *bio;
- int reads_queued, writes_queued, high_prio_read;
+ int reads_queued, writes_queued;
spin_lock(&pd->iosched.lock);
reads_queued = (pd->iosched.read_queue != NULL);
writes_queued = (pd->iosched.write_queue != NULL);
- if (!reads_queued)
- pd->iosched.high_prio_read = 0;
- high_prio_read = pd->iosched.high_prio_read;
spin_unlock(&pd->iosched.lock);
if (!reads_queued && !writes_queued)
break;
if (pd->iosched.writing) {
- if (high_prio_read || (!writes_queued && reads_queued)) {
+ int need_write_seek = 1;
+ spin_lock(&pd->iosched.lock);
+ bio = pd->iosched.write_queue;
+ spin_unlock(&pd->iosched.lock);
+ if (bio && (bio->bi_sector == pd->iosched.last_write))
+ need_write_seek = 0;
+ if (need_write_seek && reads_queued) {
if (atomic_read(&pd->cdrw.pending_bios) > 0) {
VPRINTK("pktcdvd: write, waiting\n");
break;
@@ -559,8 +561,10 @@
if (bio_data_dir(bio) == READ)
pd->iosched.successive_reads += bio->bi_size >> 10;
- else
+ else {
pd->iosched.successive_reads = 0;
+ pd->iosched.last_write = bio->bi_sector + bio_sectors(bio);
+ }
if (pd->iosched.successive_reads >= HI_SPEED_SWITCH) {
if (pd->read_speed == pd->write_speed) {
pd->read_speed = MAX_SPEED;
@@ -765,7 +769,7 @@
atomic_inc(&pkt->io_wait);
bio->bi_rw = READ;
- pkt_queue_bio(pd, bio, 0);
+ pkt_queue_bio(pd, bio);
frames_read++;
}
@@ -1062,7 +1066,7 @@
atomic_set(&pkt->io_wait, 1);
pkt->w_bio->bi_rw = WRITE;
- pkt_queue_bio(pd, pkt->w_bio, 0);
+ pkt_queue_bio(pd, pkt->w_bio);
}
static void pkt_finish_packet(struct packet_data *pkt, int uptodate)
@@ -2120,7 +2124,7 @@
cloned_bio->bi_private = psd;
cloned_bio->bi_end_io = pkt_end_io_read_cloned;
pd->stats.secs_r += bio->bi_size >> 9;
- pkt_queue_bio(pd, cloned_bio, 1);
+ pkt_queue_bio(pd, cloned_bio);
return 0;
}