Message-ID: <CACVXFVME3jpraUR8cp_i-YFYu4rk4gUCZqOi86PpCHGRrh9c_g@mail.gmail.com>
Date:   Thu, 3 Nov 2016 19:17:20 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Jens Axboe <axboe@...com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 1/4] block: add scalable completion tracking of requests

On Wed, Nov 2, 2016 at 5:05 AM, Jens Axboe <axboe@...com> wrote:
> For legacy block, we simply track them in the request queue. For
> blk-mq, we track them on a per-sw queue basis, which we can then
> sum up through the hardware queues and finally to a per device
> state.
>
> The stats are tracked in, roughly, 0.1s interval windows.
>
> Add sysfs files to display the stats.
>
> Signed-off-by: Jens Axboe <axboe@...com>
> ---
>  block/Makefile            |   2 +-
>  block/blk-core.c          |   4 +
>  block/blk-mq-sysfs.c      |  47 ++++++++++
>  block/blk-mq.c            |  14 +++
>  block/blk-mq.h            |   3 +
>  block/blk-stat.c          | 226 ++++++++++++++++++++++++++++++++++++++++++++++
>  block/blk-stat.h          |  37 ++++++++
>  block/blk-sysfs.c         |  26 ++++++
>  include/linux/blk_types.h |  16 ++++
>  include/linux/blkdev.h    |   4 +
>  10 files changed, 378 insertions(+), 1 deletion(-)
>  create mode 100644 block/blk-stat.c
>  create mode 100644 block/blk-stat.h
>
> diff --git a/block/Makefile b/block/Makefile
> index 934dac73fb37..2528c596f7ec 100644
> --- a/block/Makefile
> +++ b/block/Makefile
> @@ -5,7 +5,7 @@
>  obj-$(CONFIG_BLOCK) := bio.o elevator.o blk-core.o blk-tag.o blk-sysfs.o \
>                         blk-flush.o blk-settings.o blk-ioc.o blk-map.o \
>                         blk-exec.o blk-merge.o blk-softirq.o blk-timeout.o \
> -                       blk-lib.o blk-mq.o blk-mq-tag.o \
> +                       blk-lib.o blk-mq.o blk-mq-tag.o blk-stat.o \
>                         blk-mq-sysfs.o blk-mq-cpumap.o ioctl.o \
>                         genhd.o scsi_ioctl.o partition-generic.o ioprio.o \
>                         badblocks.o partitions/
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 0bfaa54d3e9f..ca77c725b4e5 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -2462,6 +2462,8 @@ void blk_start_request(struct request *req)
>  {
>         blk_dequeue_request(req);
>
> +       blk_stat_set_issue_time(&req->issue_stat);
> +
>         /*
>          * We are now handing the request to the hardware, initialize
>          * resid_len to full count and add the timeout handler.
> @@ -2529,6 +2531,8 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
>
>         trace_block_rq_complete(req->q, req, nr_bytes);
>
> +       blk_stat_add(&req->q->rq_stats[rq_data_dir(req)], req);

blk_update_request() is often called lockless, so it isn't good to
do it here.

> +
>         if (!req->bio)
>                 return false;
>
> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index 01fb455d3377..633c79a538ea 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/block/blk-mq-sysfs.c
> @@ -259,6 +259,47 @@ static ssize_t blk_mq_hw_sysfs_cpus_show(struct blk_mq_hw_ctx *hctx, char *page)
>         return ret;
>  }
>
> +static void blk_mq_stat_clear(struct blk_mq_hw_ctx *hctx)
> +{
> +       struct blk_mq_ctx *ctx;
> +       unsigned int i;
> +
> +       hctx_for_each_ctx(hctx, ctx, i) {
> +               blk_stat_init(&ctx->stat[0]);
> +               blk_stat_init(&ctx->stat[1]);
> +       }
> +}
> +
> +static ssize_t blk_mq_hw_sysfs_stat_store(struct blk_mq_hw_ctx *hctx,
> +                                         const char *page, size_t count)
> +{
> +       blk_mq_stat_clear(hctx);
> +       return count;
> +}
> +
> +static ssize_t print_stat(char *page, struct blk_rq_stat *stat, const char *pre)
> +{
> +       return sprintf(page, "%s samples=%llu, mean=%lld, min=%lld, max=%lld\n",
> +                       pre, (long long) stat->nr_samples,
> +                       (long long) stat->mean, (long long) stat->min,
> +                       (long long) stat->max);
> +}
> +
> +static ssize_t blk_mq_hw_sysfs_stat_show(struct blk_mq_hw_ctx *hctx, char *page)
> +{
> +       struct blk_rq_stat stat[2];
> +       ssize_t ret;
> +
> +       blk_stat_init(&stat[0]);
> +       blk_stat_init(&stat[1]);
> +
> +       blk_hctx_stat_get(hctx, stat);
> +
> +       ret = print_stat(page, &stat[0], "read :");
> +       ret += print_stat(page + ret, &stat[1], "write:");
> +       return ret;
> +}
> +
>  static struct blk_mq_ctx_sysfs_entry blk_mq_sysfs_dispatched = {
>         .attr = {.name = "dispatched", .mode = S_IRUGO },
>         .show = blk_mq_sysfs_dispatched_show,
> @@ -317,6 +358,11 @@ static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_poll = {
>         .show = blk_mq_hw_sysfs_poll_show,
>         .store = blk_mq_hw_sysfs_poll_store,
>  };
> +static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_stat = {
> +       .attr = {.name = "stats", .mode = S_IRUGO | S_IWUSR },
> +       .show = blk_mq_hw_sysfs_stat_show,
> +       .store = blk_mq_hw_sysfs_stat_store,
> +};
>
>  static struct attribute *default_hw_ctx_attrs[] = {
>         &blk_mq_hw_sysfs_queued.attr,
> @@ -327,6 +373,7 @@ static struct attribute *default_hw_ctx_attrs[] = {
>         &blk_mq_hw_sysfs_cpus.attr,
>         &blk_mq_hw_sysfs_active.attr,
>         &blk_mq_hw_sysfs_poll.attr,
> +       &blk_mq_hw_sysfs_stat.attr,
>         NULL,
>  };
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 2da1a0ee3318..4555a76d22a7 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -30,6 +30,7 @@
>  #include "blk.h"
>  #include "blk-mq.h"
>  #include "blk-mq-tag.h"
> +#include "blk-stat.h"
>
>  static DEFINE_MUTEX(all_q_mutex);
>  static LIST_HEAD(all_q_list);
> @@ -376,10 +377,19 @@ static void blk_mq_ipi_complete_request(struct request *rq)
>         put_cpu();
>  }
>
> +static void blk_mq_stat_add(struct request *rq)
> +{
> +       struct blk_rq_stat *stat = &rq->mq_ctx->stat[rq_data_dir(rq)];
> +
> +       blk_stat_add(stat, rq);
> +}
> +
>  static void __blk_mq_complete_request(struct request *rq)
>  {
>         struct request_queue *q = rq->q;
>
> +       blk_mq_stat_add(rq);

It is still possible for rqs belonging to same sw queue to complete on different
CPUs, so same issue with legacy queue.

> +
>         if (!q->softirq_done_fn)
>                 blk_mq_end_request(rq, rq->errors);
>         else
> @@ -423,6 +433,8 @@ void blk_mq_start_request(struct request *rq)
>         if (unlikely(blk_bidi_rq(rq)))
>                 rq->next_rq->resid_len = blk_rq_bytes(rq->next_rq);
>
> +       blk_stat_set_issue_time(&rq->issue_stat);
> +
>         blk_add_timer(rq);
>
>         /*
> @@ -1708,6 +1720,8 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
>                 spin_lock_init(&__ctx->lock);
>                 INIT_LIST_HEAD(&__ctx->rq_list);
>                 __ctx->queue = q;
> +               blk_stat_init(&__ctx->stat[0]);
> +               blk_stat_init(&__ctx->stat[1]);
>
>                 /* If the cpu isn't online, the cpu is mapped to first hctx */
>                 if (!cpu_online(i))
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index e5d25249028c..8cf16cb69f64 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -1,6 +1,8 @@
>  #ifndef INT_BLK_MQ_H
>  #define INT_BLK_MQ_H
>
> +#include "blk-stat.h"
> +
>  struct blk_mq_tag_set;
>
>  struct blk_mq_ctx {
> @@ -18,6 +20,7 @@ struct blk_mq_ctx {
>
>         /* incremented at completion time */
>         unsigned long           ____cacheline_aligned_in_smp rq_completed[2];
> +       struct blk_rq_stat      stat[2];
>
>         struct request_queue    *queue;
>         struct kobject          kobj;
> diff --git a/block/blk-stat.c b/block/blk-stat.c
> new file mode 100644
> index 000000000000..642afdc6d0f8
> --- /dev/null
> +++ b/block/blk-stat.c
> @@ -0,0 +1,226 @@
> +/*
> + * Block stat tracking code
> + *
> + * Copyright (C) 2016 Jens Axboe
> + */
> +#include <linux/kernel.h>
> +#include <linux/blk-mq.h>
> +
> +#include "blk-stat.h"
> +#include "blk-mq.h"
> +
> +static void blk_stat_flush_batch(struct blk_rq_stat *stat)
> +{
> +       if (!stat->nr_batch)
> +               return;
> +       if (!stat->nr_samples)
> +               stat->mean = div64_s64(stat->batch, stat->nr_batch);
> +       else {
> +               stat->mean = div64_s64((stat->mean * stat->nr_samples) +
> +                                       stat->batch,
> +                                       stat->nr_samples + stat->nr_batch);
> +       }
> +
> +       stat->nr_samples += stat->nr_batch;
> +       stat->nr_batch = stat->batch = 0;
> +}
> +
> +void blk_stat_sum(struct blk_rq_stat *dst, struct blk_rq_stat *src)
> +{
> +       if (!src->nr_samples)
> +               return;
> +
> +       blk_stat_flush_batch(src);
> +
> +       dst->min = min(dst->min, src->min);
> +       dst->max = max(dst->max, src->max);
> +
> +       if (!dst->nr_samples)
> +               dst->mean = src->mean;
> +       else {
> +               dst->mean = div64_s64((src->mean * src->nr_samples) +
> +                                       (dst->mean * dst->nr_samples),
> +                                       dst->nr_samples + src->nr_samples);
> +       }
> +       dst->nr_samples += src->nr_samples;
> +}
> +
> +static void blk_mq_stat_get(struct request_queue *q, struct blk_rq_stat *dst)
> +{
> +       struct blk_mq_hw_ctx *hctx;
> +       struct blk_mq_ctx *ctx;
> +       uint64_t latest = 0;
> +       int i, j, nr;
> +
> +       blk_stat_init(&dst[0]);
> +       blk_stat_init(&dst[1]);
> +
> +       nr = 0;
> +       do {
> +               uint64_t newest = 0;
> +
> +               queue_for_each_hw_ctx(q, hctx, i) {
> +                       hctx_for_each_ctx(hctx, ctx, j) {
> +                               if (!ctx->stat[0].nr_samples &&
> +                                   !ctx->stat[1].nr_samples)
> +                                       continue;
> +                               if (ctx->stat[0].time > newest)
> +                                       newest = ctx->stat[0].time;
> +                               if (ctx->stat[1].time > newest)
> +                                       newest = ctx->stat[1].time;
> +                       }
> +               }
> +
> +               /*
> +                * No samples
> +                */
> +               if (!newest)
> +                       break;
> +
> +               if (newest > latest)
> +                       latest = newest;
> +
> +               queue_for_each_hw_ctx(q, hctx, i) {
> +                       hctx_for_each_ctx(hctx, ctx, j) {
> +                               if (ctx->stat[0].time == newest) {
> +                                       blk_stat_sum(&dst[0], &ctx->stat[0]);
> +                                       nr++;
> +                               }
> +                               if (ctx->stat[1].time == newest) {
> +                                       blk_stat_sum(&dst[1], &ctx->stat[1]);
> +                                       nr++;
> +                               }
> +                       }
> +               }
> +               /*
> +                * If we race on finding an entry, just loop back again.
> +                * Should be very rare.
> +                */
> +       } while (!nr);
> +
> +       dst[0].time = dst[1].time = latest;
> +}
> +
> +void blk_queue_stat_get(struct request_queue *q, struct blk_rq_stat *dst)
> +{
> +       if (q->mq_ops)
> +               blk_mq_stat_get(q, dst);
> +       else {
> +               memcpy(&dst[0], &q->rq_stats[0], sizeof(struct blk_rq_stat));
> +               memcpy(&dst[1], &q->rq_stats[1], sizeof(struct blk_rq_stat));
> +       }
> +}
> +
> +void blk_hctx_stat_get(struct blk_mq_hw_ctx *hctx, struct blk_rq_stat *dst)
> +{
> +       struct blk_mq_ctx *ctx;
> +       unsigned int i, nr;
> +
> +       nr = 0;
> +       do {
> +               uint64_t newest = 0;
> +
> +               hctx_for_each_ctx(hctx, ctx, i) {
> +                       if (!ctx->stat[0].nr_samples &&
> +                           !ctx->stat[1].nr_samples)
> +                               continue;
> +
> +                       if (ctx->stat[0].time > newest)
> +                               newest = ctx->stat[0].time;
> +                       if (ctx->stat[1].time > newest)
> +                               newest = ctx->stat[1].time;
> +               }
> +
> +               if (!newest)
> +                       break;
> +
> +               hctx_for_each_ctx(hctx, ctx, i) {
> +                       if (ctx->stat[0].time == newest) {
> +                               blk_stat_sum(&dst[0], &ctx->stat[0]);
> +                               nr++;
> +                       }
> +                       if (ctx->stat[1].time == newest) {
> +                               blk_stat_sum(&dst[1], &ctx->stat[1]);
> +                               nr++;
> +                       }
> +               }
> +               /*
> +                * If we race on finding an entry, just loop back again.
> +                * Should be very rare, as the window is only updated
> +                * occasionally
> +                */
> +       } while (!nr);
> +}
> +
> +static void __blk_stat_init(struct blk_rq_stat *stat, s64 time_now)
> +{
> +       stat->min = -1ULL;
> +       stat->max = stat->nr_samples = stat->mean = 0;
> +       stat->batch = stat->nr_batch = 0;
> +       stat->time = time_now & BLK_STAT_NSEC_MASK;
> +}
> +
> +void blk_stat_init(struct blk_rq_stat *stat)
> +{
> +       __blk_stat_init(stat, ktime_to_ns(ktime_get()));
> +}
> +
> +static bool __blk_stat_is_current(struct blk_rq_stat *stat, s64 now)
> +{
> +       return (now & BLK_STAT_NSEC_MASK) == (stat->time & BLK_STAT_NSEC_MASK);
> +}
> +
> +bool blk_stat_is_current(struct blk_rq_stat *stat)
> +{
> +       return __blk_stat_is_current(stat, ktime_to_ns(ktime_get()));
> +}
> +
> +void blk_stat_add(struct blk_rq_stat *stat, struct request *rq)
> +{
> +       s64 now, value;
> +
> +       now = __blk_stat_time(ktime_to_ns(ktime_get()));
> +       if (now < blk_stat_time(&rq->issue_stat))
> +               return;
> +
> +       if (!__blk_stat_is_current(stat, now))
> +               __blk_stat_init(stat, now);
> +
> +       value = now - blk_stat_time(&rq->issue_stat);
> +       if (value > stat->max)
> +               stat->max = value;
> +       if (value < stat->min)
> +               stat->min = value;
> +
> +       if (stat->batch + value < stat->batch ||
> +           stat->nr_batch + 1 == BLK_RQ_STAT_BATCH)
> +               blk_stat_flush_batch(stat);
> +
> +       stat->batch += value;
> +       stat->nr_batch++;
> +}
> +
> +void blk_stat_clear(struct request_queue *q)
> +{
> +       if (q->mq_ops) {
> +               struct blk_mq_hw_ctx *hctx;
> +               struct blk_mq_ctx *ctx;
> +               int i, j;
> +
> +               queue_for_each_hw_ctx(q, hctx, i) {
> +                       hctx_for_each_ctx(hctx, ctx, j) {
> +                               blk_stat_init(&ctx->stat[0]);
> +                               blk_stat_init(&ctx->stat[1]);
> +                       }
> +               }
> +       } else {
> +               blk_stat_init(&q->rq_stats[0]);
> +               blk_stat_init(&q->rq_stats[1]);
> +       }
> +}
> +
> +void blk_stat_set_issue_time(struct blk_issue_stat *stat)
> +{
> +       stat->time = (stat->time & BLK_STAT_MASK) |
> +                       (ktime_to_ns(ktime_get()) & BLK_STAT_TIME_MASK);
> +}
> diff --git a/block/blk-stat.h b/block/blk-stat.h
> new file mode 100644
> index 000000000000..26b1f45dff26
> --- /dev/null
> +++ b/block/blk-stat.h
> @@ -0,0 +1,37 @@
> +#ifndef BLK_STAT_H
> +#define BLK_STAT_H
> +
> +/*
> + * ~0.13s window as a power-of-2 (2^27 nsecs)
> + */
> +#define BLK_STAT_NSEC          134217728ULL
> +#define BLK_STAT_NSEC_MASK     ~(BLK_STAT_NSEC - 1)
> +
> +/*
> + * Upper 3 bits can be used elsewhere
> + */
> +#define BLK_STAT_RES_BITS      3
> +#define BLK_STAT_SHIFT         (64 - BLK_STAT_RES_BITS)
> +#define BLK_STAT_TIME_MASK     ((1ULL << BLK_STAT_SHIFT) - 1)
> +#define BLK_STAT_MASK          ~BLK_STAT_TIME_MASK
> +
> +void blk_stat_add(struct blk_rq_stat *, struct request *);
> +void blk_hctx_stat_get(struct blk_mq_hw_ctx *, struct blk_rq_stat *);
> +void blk_queue_stat_get(struct request_queue *, struct blk_rq_stat *);
> +void blk_stat_clear(struct request_queue *q);
> +void blk_stat_init(struct blk_rq_stat *);
> +void blk_stat_sum(struct blk_rq_stat *, struct blk_rq_stat *);
> +bool blk_stat_is_current(struct blk_rq_stat *);
> +void blk_stat_set_issue_time(struct blk_issue_stat *);
> +
> +static inline u64 __blk_stat_time(u64 time)
> +{
> +       return time & BLK_STAT_TIME_MASK;
> +}
> +
> +static inline u64 blk_stat_time(struct blk_issue_stat *stat)
> +{
> +       return __blk_stat_time(stat->time);
> +}
> +
> +#endif
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 488c2e28feb8..5bb4648f434a 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -401,6 +401,26 @@ static ssize_t queue_dax_show(struct request_queue *q, char *page)
>         return queue_var_show(blk_queue_dax(q), page);
>  }
>
> +static ssize_t print_stat(char *page, struct blk_rq_stat *stat, const char *pre)
> +{
> +       return sprintf(page, "%s samples=%llu, mean=%lld, min=%lld, max=%lld\n",
> +                       pre, (long long) stat->nr_samples,
> +                       (long long) stat->mean, (long long) stat->min,
> +                       (long long) stat->max);
> +}
> +
> +static ssize_t queue_stats_show(struct request_queue *q, char *page)
> +{
> +       struct blk_rq_stat stat[2];
> +       ssize_t ret;
> +
> +       blk_queue_stat_get(q, stat);
> +
> +       ret = print_stat(page, &stat[0], "read :");
> +       ret += print_stat(page + ret, &stat[1], "write:");
> +       return ret;
> +}
> +
>  static struct queue_sysfs_entry queue_requests_entry = {
>         .attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
>         .show = queue_requests_show,
> @@ -553,6 +573,11 @@ static struct queue_sysfs_entry queue_dax_entry = {
>         .show = queue_dax_show,
>  };
>
> +static struct queue_sysfs_entry queue_stats_entry = {
> +       .attr = {.name = "stats", .mode = S_IRUGO },
> +       .show = queue_stats_show,
> +};
> +
>  static struct attribute *default_attrs[] = {
>         &queue_requests_entry.attr,
>         &queue_ra_entry.attr,
> @@ -582,6 +607,7 @@ static struct attribute *default_attrs[] = {
>         &queue_poll_entry.attr,
>         &queue_wc_entry.attr,
>         &queue_dax_entry.attr,
> +       &queue_stats_entry.attr,
>         NULL,
>  };
>
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index bb921028e7c5..a59a214c39ae 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -248,4 +248,20 @@ static inline unsigned int blk_qc_t_to_tag(blk_qc_t cookie)
>         return cookie & ((1u << BLK_QC_T_SHIFT) - 1);
>  }
>
> +struct blk_issue_stat {
> +       u64 time;
> +};
> +
> +#define BLK_RQ_STAT_BATCH      64
> +
> +struct blk_rq_stat {
> +       s64 mean;
> +       u64 min;
> +       u64 max;
> +       s32 nr_samples;
> +       s32 nr_batch;
> +       u64 batch;
> +       s64 time;
> +};
> +
>  #endif /* __LINUX_BLK_TYPES_H */
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 8396da2bb698..dcd8d6e8801f 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -197,6 +197,7 @@ struct request {
>         struct gendisk *rq_disk;
>         struct hd_struct *part;
>         unsigned long start_time;
> +       struct blk_issue_stat issue_stat;
>  #ifdef CONFIG_BLK_CGROUP
>         struct request_list *rl;                /* rl this rq is alloced from */
>         unsigned long long start_time_ns;
> @@ -490,6 +491,9 @@ struct request_queue {
>
>         unsigned int            nr_sorted;
>         unsigned int            in_flight[2];
> +
> +       struct blk_rq_stat      rq_stats[2];
> +
>         /*
>          * Number of active block driver functions for which blk_drain_queue()
>          * must wait. Must be incremented around functions that unlock the
> --
> 2.7.4
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-- 
Ming Lei

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