[Devel] Re: [PATCH] cfq: get rid of cfqq hash

[Jens Axboe]

On Wed, Apr 25 2007, Jens Axboe wrote:
> On Wed, Apr 25 2007, Vasily Tarasov wrote:
> > >> @@ -1806,7 +1765,11 @@ static int cfq_may_queue(request_queue_t
> > >>  	 * so just lookup a possibly existing queue, or return 'may queue'
> > >>  	 * if that fails
> > >>  	 */
> > >> -	cfqq = cfq_find_cfq_hash(cfqd, key, tsk->ioprio);
> > >> +	cic = cfq_get_io_context_noalloc(cfqd, tsk);
> > >> +	if (!cic)
> > >> +		return ELV_MQUEUE_MAY; 
> > >> +
> > >> +	cfqq = cic->cfqq[rw & REQ_RW_SYNC];
> > >>  	if (cfqq) {
> > >>  		cfq_init_prio_data(cfqq);
> > >>  		cfq_prio_boost(cfqq);
> > > 
> > > Ahem, how well did you test this patch?
> > 
> > Ugh, again: bio_sync() returns not only 0/1
> > Sorry for giving so much trouble...
> 
> Right, and REQ_RW_SYNC isn't 1 either, so it returns a large number if
> set.

This is also needed, you can't just rely on bio_sync(), a check for a
READ is needed as well.

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 17e4660..b793817 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -215,6 +215,18 @@ static inline void cic_set_cfqq(struct cfq_io_context *cic,
 }
 
 /*
+ * We regard a request as SYNC, if it's either a read or has the SYNC bit
+ * set (in which case it could also be direct WRITE).
+ */
+static inline int cfq_bio_sync(struct bio *bio)
+{
+	if (bio_data_dir(bio) == READ || bio_sync(bio))
+		return 1;
+
+	return 0;
+}
+
+/*
  * scheduler run of queue, if there are requests pending and no one in the
  * driver that will restart queueing
  */
@@ -594,7 +606,7 @@ cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
 	if (!cic)
 		return NULL;
 
-	cfqq =  cic_to_cfqq(cic, bio_sync(bio));
+	cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
 	if (cfqq) {
 		sector_t sector = bio->bi_sector + bio_sectors(bio);
 
@@ -694,7 +706,7 @@ static int cfq_allow_merge(request_queue_t *q, struct request *rq,
 	/*
 	 * Disallow merge of a sync bio into an async request.
 	 */
-	if ((bio_data_dir(bio) == READ || bio_sync(bio)) && !rq_is_sync(rq))
+	if (cfq_bio_sync(bio) && !rq_is_sync(rq))
 		return 0;
 
 	/*
@@ -705,7 +717,7 @@ static int cfq_allow_merge(request_queue_t *q, struct request *rq,
 	if (!cic)
 		return 0;
 
-	cfqq = cic_to_cfqq(cic, bio_sync(bio));
+	cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
 	if (cfqq == RQ_CFQQ(rq))
 		return 1;
 

-- 
Jens Axboe