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Date: Fri, 9 Apr 2010 13:44:54 -0700
From: Divyesh Shah <dpshah@...gle.com>
To: Vivek Goyal <vgoyal@...hat.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 Fri, Apr 9, 2010 at 8:32 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> 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.
Done. I'll send a patch fixing all review comments from the different patches.
>
> Can we group this function near blkiocg_update_blkio_group_dequeue_stats()
> so that we introduce on less #ifdef CONFIG_DEBUG_BLK_CGROUP.
I pulled up blkiocg_update_blkio_group_dequeue_stats() to where this
function is.
>
>> + 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.
Using your calculations from the other thread, since this is at a much
coarser granularity than ns, I'm not sure we should be worrying about
overflow here.
>
>> + 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().
Done
>
>> + 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().
Done
>
>> + 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?
The avg_queue_size stats (sum and samples) are being reset - see the
memset. The current count of how many IOs are queued should not be
reset since that will mess up the accounting and hit the BUG_ONs when
decrementing counts when the requests are dispatched.
>
> 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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