cfq: don't use icq_get_changed()

cfq caches the associated cfqq's for a given cic.  The cache needs to
be flushed if the cic's ioprio or blkcg has changed.  It is currently
done by requiring the changing action to set the respective
ICQ_*_CHANGED bit in the icq and testing it from cfq_set_request(),
which involves iterating through all the affected icqs.

All cfq wants to know is whether ioprio and/or blkcg have changed
since the last flush and can be easily achieved by just remembering
the current ioprio and blkcg ID in cic.

This patch adds cic->{ioprio|blkcg_id}, updates all ioprio users to
use the remembered value instead, and updates cfq_set_request() path
such that, instead of using icq_get_changed(), the current values are
compared against the remembered ones and trigger appropriate flush
action if not.  Condition tests are moved inside both _changed
functions which are now named check_ioprio_changed() and
check_blkcg_changed().

ioprio.h::task_ioprio*() can't be used anymore and replaced with
open-coded IOPRIO_CLASS_NONE case in cfq_async_queue_prio().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 40 insertions, 23 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9e8624e9e246..7c3893d4447a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -218,6 +218,10 @@ struct cfq_io_cq {
         struct io_cq            icq;            /* must be the first member */
         struct cfq_queue        *cfqq[2];
         struct cfq_ttime        ttime;
+        int                     ioprio;         /* the current ioprio */
+#ifdef CONFIG_CFQ_GROUP_IOSCHED
+        uint64_t                blkcg_id;       /* the current blkcg ID */
+#endif
 };
 
 /*
@@ -2568,7 +2572,7 @@ static void cfq_init_prio_data(struct cfq_queue *cfqq, struct cfq_io_cq *cic)
         if (!cfq_cfqq_prio_changed(cfqq))
                 return;
 
-        ioprio_class = IOPRIO_PRIO_CLASS(cic->icq.ioc->ioprio);
+        ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
         switch (ioprio_class) {
         default:
                 printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
@@ -2580,11 +2584,11 @@ static void cfq_init_prio_data(struct cfq_queue *cfqq, struct cfq_io_cq *cic)
                 cfqq->ioprio_class = task_nice_ioclass(tsk);
                 break;
         case IOPRIO_CLASS_RT:
-                cfqq->ioprio = task_ioprio(cic->icq.ioc);
+                cfqq->ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
                 cfqq->ioprio_class = IOPRIO_CLASS_RT;
                 break;
         case IOPRIO_CLASS_BE:
-                cfqq->ioprio = task_ioprio(cic->icq.ioc);
+                cfqq->ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
                 cfqq->ioprio_class = IOPRIO_CLASS_BE;
                 break;
         case IOPRIO_CLASS_IDLE:
@@ -2602,12 +2606,17 @@ static void cfq_init_prio_data(struct cfq_queue *cfqq, struct cfq_io_cq *cic)
         cfq_clear_cfqq_prio_changed(cfqq);
 }
 
-static void changed_ioprio(struct cfq_io_cq *cic, struct bio *bio)
+static void check_ioprio_changed(struct cfq_io_cq *cic, struct bio *bio)
 {
+        int ioprio = cic->icq.ioc->ioprio;
         struct cfq_data *cfqd = cic_to_cfqd(cic);
         struct cfq_queue *cfqq;
 
-        if (unlikely(!cfqd))
+        /*
+         * Check whether ioprio has changed.  The condition may trigger
+         * spuriously on a newly created cic but there's no harm.
+         */
+        if (unlikely(!cfqd) || likely(cic->ioprio == ioprio))
                 return;
 
         cfqq = cic->cfqq[BLK_RW_ASYNC];
@@ -2624,6 +2633,8 @@ static void changed_ioprio(struct cfq_io_cq *cic, struct bio *bio)
         cfqq = cic->cfqq[BLK_RW_SYNC];
         if (cfqq)
                 cfq_mark_cfqq_prio_changed(cfqq);
+
+        cic->ioprio = ioprio;
 }
 
 static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
@@ -2647,17 +2658,24 @@ static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 }
 
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
-static void changed_cgroup(struct cfq_io_cq *cic)
+static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
 {
-        struct cfq_queue *sync_cfqq = cic_to_cfqq(cic, 1);
         struct cfq_data *cfqd = cic_to_cfqd(cic);
-        struct request_queue *q;
+        struct cfq_queue *sync_cfqq;
+        uint64_t id;
 
-        if (unlikely(!cfqd))
-                return;
+        rcu_read_lock();
+        id = bio_blkio_cgroup(bio)->id;
+        rcu_read_unlock();
 
-        q = cfqd->queue;
+        /*
+         * Check whether blkcg has changed.  The condition may trigger
+         * spuriously on a newly created cic but there's no harm.
+         */
+        if (unlikely(!cfqd) || likely(cic->blkcg_id == id))
+                return;
 
+        sync_cfqq = cic_to_cfqq(cic, 1);
         if (sync_cfqq) {
                 /*
                  * Drop reference to sync queue. A new sync queue will be
@@ -2667,7 +2685,11 @@ static void changed_cgroup(struct cfq_io_cq *cic)
                 cic_set_cfqq(cic, NULL, 1);
                 cfq_put_queue(sync_cfqq);
         }
+
+        cic->blkcg_id = id;
 }
+#else
+static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }
 #endif  /* CONFIG_CFQ_GROUP_IOSCHED */
 
 static struct cfq_queue *
@@ -2731,6 +2753,9 @@ cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
         switch (ioprio_class) {
         case IOPRIO_CLASS_RT:
                 return &cfqd->async_cfqq[0][ioprio];
+        case IOPRIO_CLASS_NONE:
+                ioprio = IOPRIO_NORM;
+                /* fall through */
         case IOPRIO_CLASS_BE:
                 return &cfqd->async_cfqq[1][ioprio];
         case IOPRIO_CLASS_IDLE:
@@ -2744,8 +2769,8 @@ static struct cfq_queue *
 cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
               struct bio *bio, gfp_t gfp_mask)
 {
-        const int ioprio = task_ioprio(cic->icq.ioc);
-        const int ioprio_class = task_ioprio_class(cic->icq.ioc);
+        const int ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
+        const int ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
         struct cfq_queue **async_cfqq = NULL;
         struct cfq_queue *cfqq = NULL;
 
@@ -3303,21 +3328,13 @@ cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
         const int rw = rq_data_dir(rq);
         const bool is_sync = rq_is_sync(rq);
         struct cfq_queue *cfqq;
-        unsigned int changed;
 
         might_sleep_if(gfp_mask & __GFP_WAIT);
 
         spin_lock_irq(q->queue_lock);
 
-        /* handle changed notifications */
-        changed = icq_get_changed(&cic->icq);
-        if (unlikely(changed & ICQ_IOPRIO_CHANGED))
-                changed_ioprio(cic, bio);
-#ifdef CONFIG_CFQ_GROUP_IOSCHED
-        if (unlikely(changed & ICQ_CGROUP_CHANGED))
-                changed_cgroup(cic);
-#endif
-
+        check_ioprio_changed(cic, bio);
+        check_blkcg_changed(cic, bio);
 new_queue:
         cfqq = cic_to_cfqq(cic, is_sync);
         if (!cfqq || cfqq == &cfqd->oom_cfqq) {