[BLOCK] ll_rw_blk: fastpath get_request()
Originally from: Nick Piggin <nickpiggin@yahoo.com.au>
Move current_io_context out of the get_request fastpth. Also try to
streamline a few other things in this area.
Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index d4beb9a..97f4e7e 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1908,40 +1908,40 @@
{
struct request *rq = NULL;
struct request_list *rl = &q->rq;
- struct io_context *ioc = current_io_context(GFP_ATOMIC);
- int priv;
+ struct io_context *ioc = NULL;
+ int may_queue, priv;
- if (rl->count[rw]+1 >= q->nr_requests) {
- /*
- * The queue will fill after this allocation, so set it as
- * full, and mark this process as "batching". This process
- * will be allowed to complete a batch of requests, others
- * will be blocked.
- */
- if (!blk_queue_full(q, rw)) {
- ioc_set_batching(q, ioc);
- blk_set_queue_full(q, rw);
+ may_queue = elv_may_queue(q, rw, bio);
+ if (may_queue == ELV_MQUEUE_NO)
+ goto rq_starved;
+
+ if (rl->count[rw]+1 >= queue_congestion_on_threshold(q)) {
+ if (rl->count[rw]+1 >= q->nr_requests) {
+ ioc = current_io_context(GFP_ATOMIC);
+ /*
+ * The queue will fill after this allocation, so set
+ * it as full, and mark this process as "batching".
+ * This process will be allowed to complete a batch of
+ * requests, others will be blocked.
+ */
+ if (!blk_queue_full(q, rw)) {
+ ioc_set_batching(q, ioc);
+ blk_set_queue_full(q, rw);
+ } else {
+ if (may_queue != ELV_MQUEUE_MUST
+ && !ioc_batching(q, ioc)) {
+ /*
+ * The queue is full and the allocating
+ * process is not a "batcher", and not
+ * exempted by the IO scheduler
+ */
+ goto out;
+ }
+ }
}
+ set_queue_congested(q, rw);
}
- switch (elv_may_queue(q, rw, bio)) {
- case ELV_MQUEUE_NO:
- goto rq_starved;
- case ELV_MQUEUE_MAY:
- break;
- case ELV_MQUEUE_MUST:
- goto get_rq;
- }
-
- if (blk_queue_full(q, rw) && !ioc_batching(q, ioc)) {
- /*
- * The queue is full and the allocating process is not a
- * "batcher", and not exempted by the IO scheduler
- */
- goto out;
- }
-
-get_rq:
/*
* Only allow batching queuers to allocate up to 50% over the defined
* limit of requests, otherwise we could have thousands of requests
@@ -1952,8 +1952,6 @@
rl->count[rw]++;
rl->starved[rw] = 0;
- if (rl->count[rw] >= queue_congestion_on_threshold(q))
- set_queue_congested(q, rw);
priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
if (priv)
@@ -1962,7 +1960,7 @@
spin_unlock_irq(q->queue_lock);
rq = blk_alloc_request(q, rw, bio, priv, gfp_mask);
- if (!rq) {
+ if (unlikely(!rq)) {
/*
* Allocation failed presumably due to memory. Undo anything
* we might have messed up.
@@ -1987,6 +1985,12 @@
goto out;
}
+ /*
+ * ioc may be NULL here, and ioc_batching will be false. That's
+ * OK, if the queue is under the request limit then requests need
+ * not count toward the nr_batch_requests limit. There will always
+ * be some limit enforced by BLK_BATCH_TIME.
+ */
if (ioc_batching(q, ioc))
ioc->nr_batch_requests--;