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Date:   Mon, 12 Dec 2022 21:40:40 +0800
From:   Chao Yu <chao@...nel.org>
To:     Yangtao Li <frank.li@...o.com>, jaegeuk@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: add support for counting time of submit discard
 cmd

On 2022/12/12 20:51, Yangtao Li wrote:
> This patch adds support for counting the average time and
> peak time of submit discard command, and we can see its
> value in debugfs.
> 
> It is not sure whether the block layer has recorded these
> data, and these data are allowed to be accessed by fs,
> or they are only exported to user space.
> 
> On the one hand, I added these data to better understand
> the current device operating status, and to further control
> the discard process in a more detailed manner based on the
> discard submit time in the future.

Again, w'd better to consider this functionality only when DEBUG_FS is
enabled.

> 
> Signed-off-by: Yangtao Li <frank.li@...o.com>
> ---
>   fs/f2fs/debug.c   | 10 +++++++---
>   fs/f2fs/f2fs.h    |  6 ++++++
>   fs/f2fs/segment.c | 21 +++++++++++++++++++--
>   3 files changed, 32 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
> index 32af4f0c5735..142c256b89d9 100644
> --- a/fs/f2fs/debug.c
> +++ b/fs/f2fs/debug.c
> @@ -120,6 +120,10 @@ 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->discard_peak = dcc->discard_time_peak;
>   		si->nr_discarded =
>   			atomic_read(&SM_I(sbi)->dcc_info->issued_discard);
>   		si->nr_discarding =
> @@ -545,9 +549,9 @@ 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,
> -			   si->nr_discard_cmd, si->undiscard_blks);
> +		seq_printf(s, "Discard: (%4d %4d, avg:%4lldns, peak:%4lldns)) cmd: %4d undiscard:%4u\n",
> +			   si->nr_discarding, si->nr_discarded, ktime_to_us(si->discard_avg),
> +			   ktime_to_us(si->discard_peak), si->nr_discard_cmd, si->undiscard_blks);
>   		seq_printf(s, "  - atomic IO: %4d (Max. %4d)\n",
>   			   si->aw_cnt, si->max_aw_cnt);
>   		seq_printf(s, "  - compress: %4d, hit:%8d\n", si->compress_pages, si->compress_page_hit);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index e8953c3dc81a..2cd55cb981ff 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -371,6 +371,8 @@ 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 {
> @@ -415,6 +417,9 @@ 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 */
> +	ktime_t discard_time_peak;		/* issued discard cmd peak time */
>   	atomic_t issued_discard;		/* # of issued discard */
>   	atomic_t queued_discard;		/* # of queued discard */
>   	atomic_t discard_cmd_cnt;		/* # of cached cmd count */
> @@ -3896,6 +3901,7 @@ 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, discard_peak;
>   	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 a9099a754dd2..73cd05bb3f4a 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -937,6 +937,7 @@ 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;
>   
> @@ -1006,9 +1007,13 @@ 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--;
> @@ -1018,6 +1023,16 @@ 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);
> +	if (dcc->discard_time_avg > dcc->discard_time_peak)
> +		dcc->discard_time_peak = dcc->discard_time_avg;
> +	atomic_inc(&dcc->issued_discard);
> +	spin_unlock_irqrestore(&dcc->discard_time_lock, flags);

Why not calculating average time only in update_general_status()? and here,
we just need to account total_{discard_time, discard_count} w/o additional
spinlock.

Thanks,

>   }
>   
>   static void __check_sit_bitmap(struct f2fs_sb_info *sbi,
> @@ -1166,6 +1181,7 @@ 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
> @@ -1185,8 +1201,6 @@ 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, len * F2FS_BLKSIZE);
>   
>   		lstart += len;
> @@ -2079,9 +2093,12 @@ 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->discard_time_peak = 0;
>   	dcc->nr_discards = 0;
>   	dcc->max_discards = MAIN_SEGS(sbi) << sbi->log_blocks_per_seg;
>   	dcc->max_discard_request = DEF_MAX_DISCARD_REQUEST;

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