From df5fe3e8e13883f58dc97489076bbcc150789a21 Mon Sep 17 00:00:00 2001 From: Jeff Moyer Date: Fri, 23 Oct 2009 17:14:50 -0400 Subject: [PATCH] cfq: merge cooperating cfq_queues When cooperating cfq_queues are detected currently, they are allowed to skip ahead in the scheduling order. It is much more efficient to automatically share the cfq_queue data structure between cooperating processes. Performance of the read-test2 benchmark (which is written to emulate the dump(8) utility) went from 12MB/s to 90MB/s on my SATA disk. NFS servers with multiple nfsd threads also saw performance increases. Signed-off-by: Jeff Moyer Signed-off-by: Jens Axboe --- block/cfq-iosched.c | 89 ++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 87 insertions(+), 2 deletions(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 78cc8ee5da41..f0994aedb390 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -118,6 +118,8 @@ struct cfq_queue { sector_t last_request_pos; pid_t pid; + + struct cfq_queue *new_cfqq; }; /* @@ -1047,6 +1049,12 @@ static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd, if (!cfqq) return NULL; + /* + * It only makes sense to merge sync queues. + */ + if (!cfq_cfqq_sync(cfqq)) + return NULL; + if (cfq_cfqq_coop(cfqq)) return NULL; @@ -1167,6 +1175,43 @@ cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq) return 2 * (base_rq + base_rq * (CFQ_PRIO_LISTS - 1 - cfqq->ioprio)); } +/* + * Must be called with the queue_lock held. + */ +static int cfqq_process_refs(struct cfq_queue *cfqq) +{ + int process_refs, io_refs; + + io_refs = cfqq->allocated[READ] + cfqq->allocated[WRITE]; + process_refs = atomic_read(&cfqq->ref) - io_refs; + BUG_ON(process_refs < 0); + return process_refs; +} + +static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq) +{ + int process_refs; + struct cfq_queue *__cfqq; + + /* Avoid a circular list and skip interim queue merges */ + while ((__cfqq = new_cfqq->new_cfqq)) { + if (__cfqq == cfqq) + return; + new_cfqq = __cfqq; + } + + process_refs = cfqq_process_refs(cfqq); + /* + * If the process for the cfqq has gone away, there is no + * sense in merging the queues. + */ + if (process_refs == 0) + return; + + cfqq->new_cfqq = new_cfqq; + atomic_add(process_refs, &new_cfqq->ref); +} + /* * Select a queue for service. If we have a current active queue, * check whether to continue servicing it, or retrieve and set a new one. @@ -1196,11 +1241,14 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd) * If another queue has a request waiting within our mean seek * distance, let it run. The expire code will check for close * cooperators and put the close queue at the front of the service - * tree. + * tree. If possible, merge the expiring queue with the new cfqq. */ new_cfqq = cfq_close_cooperator(cfqd, cfqq, 0); - if (new_cfqq) + if (new_cfqq) { + if (!cfqq->new_cfqq) + cfq_setup_merge(cfqq, new_cfqq); goto expire; + } /* * No requests pending. If the active queue still has requests in @@ -1511,11 +1559,29 @@ static void cfq_free_io_context(struct io_context *ioc) static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq) { + struct cfq_queue *__cfqq, *next; + if (unlikely(cfqq == cfqd->active_queue)) { __cfq_slice_expired(cfqd, cfqq, 0); cfq_schedule_dispatch(cfqd); } + /* + * If this queue was scheduled to merge with another queue, be + * sure to drop the reference taken on that queue (and others in + * the merge chain). See cfq_setup_merge and cfq_merge_cfqqs. + */ + __cfqq = cfqq->new_cfqq; + while (__cfqq) { + if (__cfqq == cfqq) { + WARN(1, "cfqq->new_cfqq loop detected\n"); + break; + } + next = __cfqq->new_cfqq; + cfq_put_queue(__cfqq); + __cfqq = next; + } + cfq_put_queue(cfqq); } @@ -2323,6 +2389,16 @@ static void cfq_put_request(struct request *rq) } } +static struct cfq_queue * +cfq_merge_cfqqs(struct cfq_data *cfqd, struct cfq_io_context *cic, + struct cfq_queue *cfqq) +{ + cfq_log_cfqq(cfqd, cfqq, "merging with queue %p", cfqq->new_cfqq); + cic_set_cfqq(cic, cfqq->new_cfqq, 1); + cfq_put_queue(cfqq); + return cic_to_cfqq(cic, 1); +} + /* * Allocate cfq data structures associated with this request. */ @@ -2349,6 +2425,15 @@ cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask) if (!cfqq || cfqq == &cfqd->oom_cfqq) { cfqq = cfq_get_queue(cfqd, is_sync, cic->ioc, gfp_mask); cic_set_cfqq(cic, cfqq, is_sync); + } else { + /* + * Check to see if this queue is scheduled to merge with + * another, closely cooperating queue. The merging of + * queues happens here as it must be done in process context. + * The reference on new_cfqq was taken in merge_cfqqs. + */ + if (cfqq->new_cfqq) + cfqq = cfq_merge_cfqqs(cfqd, cic, cfqq); } cfqq->allocated[rw]++; -- GitLab