Date:   Fri, 9 Dec 2022 11:59:52 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Yangtao Li <frank.li@...o.com>
Cc:     chao@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] f2fs: add support for counting the average time of
 submit discard cmd

On 11/29, Yangtao Li wrote:
> This patch adds support for counting the average time of submit discard
> command, and we can see its value in debugfs.

What about peak latencies as well?

> 
> Signed-off-by: Yangtao Li <frank.li@...o.com>
> ---
>  fs/f2fs/debug.c   |  7 +++++--
>  fs/f2fs/f2fs.h    |  5 +++++
>  fs/f2fs/segment.c | 18 ++++++++++++++++--
>  3 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
> index 733b1bd37404..eed3edfc5faf 100644
> --- a/fs/f2fs/debug.c
> +++ b/fs/f2fs/debug.c
> @@ -109,6 +109,9 @@ static void update_general_status(struct f2fs_sb_info *sbi)
>  			llist_empty(&SM_I(sbi)->fcc_info->issue_list);
>  	}
>  	if (SM_I(sbi)->dcc_info) {
> +		struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> +
> +		si->discard_avg = dcc->discard_time_avg;
>  		si->nr_discarded =
>  			atomic_read(&SM_I(sbi)->dcc_info->issued_discard);
>  		si->nr_discarding =
> @@ -510,8 +513,8 @@ static int stat_show(struct seq_file *s, void *v)
>  			   si->nr_wb_cp_data, si->nr_wb_data,
>  			   si->nr_flushing, si->nr_flushed,
>  			   si->flush_list_empty);
> -		seq_printf(s, "Discard: (%4d %4d)) cmd: %4d undiscard:%4u\n",
> -			   si->nr_discarding, si->nr_discarded,
> +		seq_printf(s, "Discard: (%4d %4d, avg:%4lldns)) cmd: %4d undiscard:%4u\n",
> +			   si->nr_discarding, si->nr_discarded, ktime_to_us(si->discard_avg),
>  			   si->nr_discard_cmd, si->undiscard_blks);
>  		seq_printf(s, "  - atomic IO: %4d (Max. %4d)\n",
>  			   si->aw_cnt, si->max_aw_cnt);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index eb8c27c4e5fc..5a99759d10ac 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -370,6 +370,8 @@ struct discard_cmd {
>  	int error;			/* bio error */
>  	spinlock_t lock;		/* for state/bio_ref updating */
>  	unsigned short bio_ref;		/* bio reference count */
> +	struct discard_cmd_control *dcc; /* global discard cmd control */
> +	ktime_t submit_start;		/* submit start time */
>  };
>  
>  enum {
> @@ -414,6 +416,8 @@ struct discard_cmd_control {
>  	unsigned int max_ordered_discard;	/* maximum discard granularity issued by lba order */
>  	unsigned int undiscard_blks;		/* # of undiscard blocks */
>  	unsigned int next_pos;			/* next discard position */
> +	spinlock_t discard_time_lock;	/* for discard time statistics */
> +	ktime_t discard_time_avg;		/* issued discard cmd avg time */
>  	atomic_t issued_discard;		/* # of issued discard */
>  	atomic_t queued_discard;		/* # of queued discard */
>  	atomic_t discard_cmd_cnt;		/* # of cached cmd count */
> @@ -3882,6 +3886,7 @@ struct f2fs_stat_info {
>  	int nr_dio_read, nr_dio_write;
>  	unsigned int io_skip_bggc, other_skip_bggc;
>  	int nr_flushing, nr_flushed, flush_list_empty;
> +	ktime_t	discard_avg;
>  	int nr_discarding, nr_discarded;
>  	int nr_discard_cmd;
>  	unsigned int undiscard_blks;
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 9486ca49ecb1..bc96b1afb308 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -931,6 +931,7 @@ static struct discard_cmd *__create_discard_cmd(struct f2fs_sb_info *sbi,
>  	list_add_tail(&dc->list, pend_list);
>  	spin_lock_init(&dc->lock);
>  	dc->bio_ref = 0;
> +	dc->dcc = dcc;
>  	atomic_inc(&dcc->discard_cmd_cnt);
>  	dcc->undiscard_blks += len;
>  
> @@ -1000,9 +1001,13 @@ static void __remove_discard_cmd(struct f2fs_sb_info *sbi,
>  static void f2fs_submit_discard_endio(struct bio *bio)
>  {
>  	struct discard_cmd *dc = (struct discard_cmd *)bio->bi_private;
> +	struct discard_cmd_control *dcc = dc->dcc;
>  	unsigned long flags;
> +	ktime_t submit_time;
> +	int nr_discarded;
>  
>  	spin_lock_irqsave(&dc->lock, flags);
> +	submit_time = ktime_sub(ktime_get(), dc->submit_start);
>  	if (!dc->error)
>  		dc->error = blk_status_to_errno(bio->bi_status);
>  	dc->bio_ref--;
> @@ -1012,6 +1017,14 @@ static void f2fs_submit_discard_endio(struct bio *bio)
>  	}
>  	spin_unlock_irqrestore(&dc->lock, flags);
>  	bio_put(bio);
> +
> +	spin_lock_irqsave(&dcc->discard_time_lock, flags);
> +	nr_discarded = atomic_read(&dcc->issued_discard);
> +	dcc->discard_time_avg = div_u64(ktime_add(nr_discarded * dcc->discard_time_avg,
> +										submit_time),
> +									nr_discarded + 1);
> +	atomic_inc(&dcc->issued_discard);
> +	spin_unlock_irqrestore(&dcc->discard_time_lock, flags);
>  }
>  
>  static void __check_sit_bitmap(struct f2fs_sb_info *sbi,
> @@ -1160,6 +1173,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  		 * right away
>  		 */
>  		spin_lock_irqsave(&dc->lock, flags);
> +		dc->submit_start = ktime_get();
>  		if (last)
>  			dc->state = D_SUBMIT;
>  		else
> @@ -1179,8 +1193,6 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  		bio->bi_opf |= flag;
>  		submit_bio(bio);
>  
> -		atomic_inc(&dcc->issued_discard);
> -
>  		f2fs_update_iostat(sbi, NULL, FS_DISCARD, 1);
>  
>  		lstart += len;
> @@ -2070,9 +2082,11 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
>  	INIT_LIST_HEAD(&dcc->wait_list);
>  	INIT_LIST_HEAD(&dcc->fstrim_list);
>  	mutex_init(&dcc->cmd_lock);
> +	spin_lock_init(&dcc->discard_time_lock);
>  	atomic_set(&dcc->issued_discard, 0);
>  	atomic_set(&dcc->queued_discard, 0);
>  	atomic_set(&dcc->discard_cmd_cnt, 0);
> +	dcc->discard_time_avg = 0;
>  	dcc->nr_discards = 0;
>  	dcc->max_discards = MAIN_SEGS(sbi) << sbi->log_blocks_per_seg;
>  	dcc->max_discard_request = DEF_MAX_DISCARD_REQUEST;
> -- 
> 2.25.1

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