Re: [PATCH v2] f2fs: add support for counting time of submit discard cmd

[Chao Yu]

On 2022/12/13 6:47, Jaegeuk Kim wrote:
> On 12/12, Chao Yu wrote:
> > 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.
>
> BTW, why can't we use iostat to get the discard latencies?

Agreed.

Thanks,

> > > Signed-off-by: Yangtao Li <frank.li@xxxxxxxx>
> > > ---
> > >    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;