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Message-ID: <0cc89bf7-ea7c-d6e9-5ba9-548181de4c82@kernel.org>
Date: Tue, 13 Dec 2022 09:22:09 +0800
From: Chao Yu <chao@...nel.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: Yangtao Li <frank.li@...o.com>,
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 2022/12/13 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@...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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