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Date: Fri, 9 Apr 2010 11:32:55 -0400
From: Vivek Goyal <vgoyal@...hat.com>
To: Divyesh Shah <dpshah@...gle.com>
Cc: jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
nauman@...gle.com, ctalbott@...gle.com
Subject: Re: [PATCH 2/3] blkio: Add io_queued and avg_queue_size stats
On Thu, Apr 08, 2010 at 09:15:10PM -0700, Divyesh Shah wrote:
> These stats are useful for getting a feel for the queue depth of the cgroup,
> i.e., how filled up its queues are at a given instant and over the existence of
> the cgroup. This ability is useful when debugging problems in the wild as it
> helps understand the application's IO pattern w/o having to read through the
> userspace code (coz its tedious or just not available) or w/o the ability
> to run blktrace (since you may not have root access and/or not want to disturb
> performance).
>
> Signed-off-by: Divyesh Shah<dpshah@...gle.com>
> ---
>
> Documentation/cgroups/blkio-controller.txt | 11 +++
> block/blk-cgroup.c | 98 +++++++++++++++++++++++++++-
> block/blk-cgroup.h | 20 +++++-
> block/cfq-iosched.c | 11 +++
> 4 files changed, 134 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
> index 810e301..6e52e7c 100644
> --- a/Documentation/cgroups/blkio-controller.txt
> +++ b/Documentation/cgroups/blkio-controller.txt
> @@ -139,6 +139,17 @@ Details of cgroup files
> cgroup. This is further divided by the type of operation - read or
> write, sync or async.
>
> +- blkio.io_queued
> + - Total number of requests queued up at any given instant for this
> + cgroup. This is further divided by the type of operation - read or
> + write, sync or async.
> +
> +- blkio.avg_queue_size
> + - Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y.
> + The average queue size for this cgroup over the entire time of this
> + cgroup's existence. Queue size samples are taken each time one of the
> + queues of this cgroup gets a timeslice.
> +
> - blkio.dequeue
> - Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y. This
> gives the statistics about how many a times a group was dequeued
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index d23b538..1e0c497 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -81,6 +81,71 @@ static void blkio_add_stat(uint64_t *stat, uint64_t add, bool direction,
> stat[BLKIO_STAT_ASYNC] += add;
> }
>
> +/*
> + * Decrements the appropriate stat variable if non-zero depending on the
> + * request type. Panics on value being zero.
> + * This should be called with the blkg->stats_lock held.
> + */
> +static void blkio_check_and_dec_stat(uint64_t *stat, bool direction, bool sync)
> +{
> + if (direction) {
> + BUG_ON(stat[BLKIO_STAT_WRITE] == 0);
> + stat[BLKIO_STAT_WRITE]--;
> + } else {
> + BUG_ON(stat[BLKIO_STAT_READ] == 0);
> + stat[BLKIO_STAT_READ]--;
> + }
> + if (sync) {
> + BUG_ON(stat[BLKIO_STAT_SYNC] == 0);
> + stat[BLKIO_STAT_SYNC]--;
> + } else {
> + BUG_ON(stat[BLKIO_STAT_ASYNC] == 0);
> + stat[BLKIO_STAT_ASYNC]--;
> + }
> +}
> +
> +#ifdef CONFIG_DEBUG_BLK_CGROUP
> +void blkiocg_update_set_active_queue_stats(struct blkio_group *blkg)
> +{
How about blkiocg_update_avg_queue_size_stats()? A different io policy can
choose to take this sample at higher rate and not necessarily when
queue is set active.
Can we group this function near blkiocg_update_blkio_group_dequeue_stats()
so that we introduce on less #ifdef CONFIG_DEBUG_BLK_CGROUP.
> + unsigned long flags;
> + struct blkio_group_stats *stats;
> +
> + spin_lock_irqsave(&blkg->stats_lock, flags);
> + stats = &blkg->stats;
> + stats->avg_queue_size_sum +=
> + stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_READ] +
> + stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_WRITE];
> + stats->avg_queue_size_samples++;
What happens when over a period of time "avg_queue_size_sum" or "avg_queue_size_samples" overflow? All the stats will look weird.
> + spin_unlock_irqrestore(&blkg->stats_lock, flags);
> +}
> +EXPORT_SYMBOL_GPL(blkiocg_update_set_active_queue_stats);
> +#endif
> +
> +void blkiocg_update_request_add_stats(struct blkio_group *blkg,
> + struct blkio_group *curr_blkg, bool direction,
> + bool sync)
> +{
curr_blkg is redundant?
How about just use "io" keyword instead of "request" as you have been
doing all along. blkiocg_update_io_add_stats().
> + unsigned long flags;
> +
> + spin_lock_irqsave(&blkg->stats_lock, flags);
> + blkio_add_stat(blkg->stats.stat_arr[BLKIO_STAT_QUEUED], 1, direction,
> + sync);
> + spin_unlock_irqrestore(&blkg->stats_lock, flags);
> +}
> +EXPORT_SYMBOL_GPL(blkiocg_update_request_add_stats);
> +
> +void blkiocg_update_request_remove_stats(struct blkio_group *blkg,
> + bool direction, bool sync)
> +{
blkiocg_update_io_remove_stats().
> + unsigned long flags;
> +
> + spin_lock_irqsave(&blkg->stats_lock, flags);
> + blkio_check_and_dec_stat(blkg->stats.stat_arr[BLKIO_STAT_QUEUED],
> + direction, sync);
> + spin_unlock_irqrestore(&blkg->stats_lock, flags);
> +}
> +EXPORT_SYMBOL_GPL(blkiocg_update_request_remove_stats);
> +
> void blkiocg_update_timeslice_used(struct blkio_group *blkg, unsigned long time)
> {
> unsigned long flags;
> @@ -253,14 +318,18 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
> struct blkio_cgroup *blkcg;
> struct blkio_group *blkg;
> struct hlist_node *n;
> - struct blkio_group_stats *stats;
> + uint64_t queued[BLKIO_STAT_TOTAL];
> + int i;
>
> blkcg = cgroup_to_blkio_cgroup(cgroup);
> spin_lock_irq(&blkcg->lock);
> hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
> spin_lock(&blkg->stats_lock);
> - stats = &blkg->stats;
> - memset(stats, 0, sizeof(struct blkio_group_stats));
> + for (i = 0; i < BLKIO_STAT_TOTAL; i++)
> + queued[i] = blkg->stats.stat_arr[BLKIO_STAT_QUEUED][i];
> + memset(&blkg->stats, 0, sizeof(struct blkio_group_stats));
> + for (i = 0; i < BLKIO_STAT_TOTAL; i++)
> + blkg->stats.stat_arr[BLKIO_STAT_QUEUED][i] = queued[i];
During reset_stats, why are you not resetting the stats for average queue
depth? This reset_stat is mean to reset all the debug stats we have
collected so far for the cgroup?
Thanks
Vivek
> spin_unlock(&blkg->stats_lock);
> }
> spin_unlock_irq(&blkcg->lock);
> @@ -323,6 +392,15 @@ static uint64_t blkio_get_stat(struct blkio_group *blkg,
> return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
> blkg->stats.sectors, cb, dev);
> #ifdef CONFIG_DEBUG_BLK_CGROUP
> + if (type == BLKIO_STAT_AVG_QUEUE_SIZE) {
> + uint64_t sum = blkg->stats.avg_queue_size_sum;
> + uint64_t samples = blkg->stats.avg_queue_size_samples;
> + if (samples)
> + do_div(sum, samples);
> + else
> + sum = 0;
> + return blkio_fill_stat(key_str, MAX_KEY_LEN - 1, sum, cb, dev);
> + }
> if (type == BLKIO_STAT_DEQUEUE)
> return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
> blkg->stats.dequeue, cb, dev);
> @@ -376,8 +454,10 @@ SHOW_FUNCTION_PER_GROUP(io_serviced, BLKIO_STAT_SERVICED, 1);
> SHOW_FUNCTION_PER_GROUP(io_service_time, BLKIO_STAT_SERVICE_TIME, 1);
> SHOW_FUNCTION_PER_GROUP(io_wait_time, BLKIO_STAT_WAIT_TIME, 1);
> SHOW_FUNCTION_PER_GROUP(io_merged, BLKIO_STAT_MERGED, 1);
> +SHOW_FUNCTION_PER_GROUP(io_queued, BLKIO_STAT_QUEUED, 1);
> #ifdef CONFIG_DEBUG_BLK_CGROUP
> SHOW_FUNCTION_PER_GROUP(dequeue, BLKIO_STAT_DEQUEUE, 0);
> +SHOW_FUNCTION_PER_GROUP(avg_queue_size, BLKIO_STAT_AVG_QUEUE_SIZE, 0);
> #endif
> #undef SHOW_FUNCTION_PER_GROUP
>
> @@ -425,14 +505,22 @@ struct cftype blkio_files[] = {
> .read_map = blkiocg_io_merged_read,
> },
> {
> + .name = "io_queued",
> + .read_map = blkiocg_io_queued_read,
> + },
> + {
> .name = "reset_stats",
> .write_u64 = blkiocg_reset_stats,
> },
> #ifdef CONFIG_DEBUG_BLK_CGROUP
> - {
> + {
> + .name = "avg_queue_size",
> + .read_map = blkiocg_avg_queue_size_read,
> + },
> + {
> .name = "dequeue",
> .read_map = blkiocg_dequeue_read,
> - },
> + },
> #endif
> };
>
> diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
> index 470a29d..bea7f3b 100644
> --- a/block/blk-cgroup.h
> +++ b/block/blk-cgroup.h
> @@ -36,10 +36,13 @@ enum stat_type {
> BLKIO_STAT_WAIT_TIME,
> /* Number of IOs merged */
> BLKIO_STAT_MERGED,
> + /* Number of IOs queued up */
> + BLKIO_STAT_QUEUED,
> /* All the single valued stats go below this */
> BLKIO_STAT_TIME,
> BLKIO_STAT_SECTORS,
> #ifdef CONFIG_DEBUG_BLK_CGROUP
> + BLKIO_STAT_AVG_QUEUE_SIZE,
> BLKIO_STAT_DEQUEUE
> #endif
> };
> @@ -63,8 +66,12 @@ struct blkio_group_stats {
> /* total disk time and nr sectors dispatched by this group */
> uint64_t time;
> uint64_t sectors;
> - uint64_t stat_arr[BLKIO_STAT_MERGED + 1][BLKIO_STAT_TOTAL];
> + uint64_t stat_arr[BLKIO_STAT_QUEUED + 1][BLKIO_STAT_TOTAL];
> #ifdef CONFIG_DEBUG_BLK_CGROUP
> + /* Sum of number of IOs queued across all samples */
> + uint64_t avg_queue_size_sum;
> + /* Count of samples taken for average */
> + uint64_t avg_queue_size_samples;
> /* How many times this group has been removed from service tree */
> unsigned long dequeue;
> #endif
> @@ -127,10 +134,13 @@ static inline char *blkg_path(struct blkio_group *blkg)
> {
> return blkg->path;
> }
> +void blkiocg_update_set_active_queue_stats(struct blkio_group *blkg);
> void blkiocg_update_dequeue_stats(struct blkio_group *blkg,
> unsigned long dequeue);
> #else
> static inline char *blkg_path(struct blkio_group *blkg) { return NULL; }
> +static inline void blkiocg_update_set_active_queue_stats(
> + struct blkio_group *blkg) {}
> static inline void blkiocg_update_dequeue_stats(struct blkio_group *blkg,
> unsigned long dequeue) {}
> #endif
> @@ -152,6 +162,10 @@ void blkiocg_update_completion_stats(struct blkio_group *blkg,
> uint64_t start_time, uint64_t io_start_time, bool direction, bool sync);
> void blkiocg_update_io_merged_stats(struct blkio_group *blkg, bool direction,
> bool sync);
> +void blkiocg_update_request_add_stats(struct blkio_group *blkg,
> + struct blkio_group *curr_blkg, bool direction, bool sync);
> +void blkiocg_update_request_remove_stats(struct blkio_group *blkg,
> + bool direction, bool sync);
> #else
> struct cgroup;
> static inline struct blkio_cgroup *
> @@ -175,5 +189,9 @@ static inline void blkiocg_update_completion_stats(struct blkio_group *blkg,
> bool sync) {}
> static inline void blkiocg_update_io_merged_stats(struct blkio_group *blkg,
> bool direction, bool sync) {}
> +static inline void blkiocg_update_request_add_stats(struct blkio_group *blkg,
> + struct blkio_group *curr_blkg, bool direction, bool sync) {}
> +static inline void blkiocg_update_request_remove_stats(struct blkio_group *blkg,
> + bool direction, bool sync) {}
> #endif
> #endif /* _BLK_CGROUP_H */
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 4eb1906..8e0b86a 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -1380,7 +1380,12 @@ static void cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)
> {
> elv_rb_del(&cfqq->sort_list, rq);
> cfqq->queued[rq_is_sync(rq)]--;
> + blkiocg_update_request_remove_stats(&cfqq->cfqg->blkg, rq_data_dir(rq),
> + rq_is_sync(rq));
> cfq_add_rq_rb(rq);
> + blkiocg_update_request_add_stats(
> + &cfqq->cfqg->blkg, &cfqq->cfqd->serving_group->blkg,
> + rq_data_dir(rq), rq_is_sync(rq));
> }
>
> static struct request *
> @@ -1436,6 +1441,8 @@ static void cfq_remove_request(struct request *rq)
> cfq_del_rq_rb(rq);
>
> cfqq->cfqd->rq_queued--;
> + blkiocg_update_request_remove_stats(&cfqq->cfqg->blkg, rq_data_dir(rq),
> + rq_is_sync(rq));
> if (rq_is_meta(rq)) {
> WARN_ON(!cfqq->meta_pending);
> cfqq->meta_pending--;
> @@ -1527,6 +1534,7 @@ static void __cfq_set_active_queue(struct cfq_data *cfqd,
> if (cfqq) {
> cfq_log_cfqq(cfqd, cfqq, "set_active wl_prio:%d wl_type:%d",
> cfqd->serving_prio, cfqd->serving_type);
> + blkiocg_update_set_active_queue_stats(&cfqq->cfqg->blkg);
> cfqq->slice_start = 0;
> cfqq->dispatch_start = jiffies;
> cfqq->allocated_slice = 0;
> @@ -3213,6 +3221,9 @@ static void cfq_insert_request(struct request_queue *q, struct request *rq)
> list_add_tail(&rq->queuelist, &cfqq->fifo);
> cfq_add_rq_rb(rq);
>
> + blkiocg_update_request_add_stats(&cfqq->cfqg->blkg,
> + &cfqd->serving_group->blkg, rq_data_dir(rq),
> + rq_is_sync(rq));
> cfq_rq_enqueued(cfqd, cfqq, rq);
> }
>
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