Re: [PATCH v3 1/5] wbt: don't show valid wbt_lat_usec in sysfs while wbt is disabled

From: Jan Kara <jack@suse.cz>
To: Yu Kuai <yukuai3@huawei.com>
Cc: jack@suse.cz, paolo.valente@linaro.org, axboe@kernel.dk,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	yukuai1@huaweicloud.com, yi.zhang@huawei.com
Subject: Re: [PATCH v3 1/5] wbt: don't show valid wbt_lat_usec in sysfs while wbt is disabled
Date: Mon, 26 Sep 2022 11:44:34 +0200	[thread overview]
Message-ID: <20220926094434.jrl6gnlbjqkex3wa@quack3> (raw)
In-Reply-To: <20220922113558.1085314-2-yukuai3@huawei.com>

On Thu 22-09-22 19:35:54, Yu Kuai wrote:
> Currently, if wbt is initialized and then disabled by
> wbt_disable_default(), sysfs will still show valid wbt_lat_usec, which
> will confuse users that wbt is still enabled.
> 
> This patch shows wbt_lat_usec as zero and forbid to set it while wbt
> is disabled.

So I agree we should show 0 in wbt_lat_usec if wbt is disabled by
wbt_disable_default(). But why do you forbid setting of wbt_lat_usec?
IMHO if wbt_lat_usec is set, admin wants to turn on wbt so we should just
update rwb->enable_state to WBT_STATE_ON_MANUAL.

								Honza

> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> Reported-and-tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
> ---
>  block/blk-sysfs.c | 9 ++++++++-
>  block/blk-wbt.c   | 7 +++++++
>  block/blk-wbt.h   | 5 +++++
>  3 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index e1f009aba6fd..1955bb6a284d 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -467,10 +467,14 @@ static ssize_t queue_io_timeout_store(struct request_queue *q, const char *page,
>  
>  static ssize_t queue_wb_lat_show(struct request_queue *q, char *page)
>  {
> +	u64 lat;
> +
>  	if (!wbt_rq_qos(q))
>  		return -EINVAL;
>  
> -	return sprintf(page, "%llu\n", div_u64(wbt_get_min_lat(q), 1000));
> +	lat = wbt_disabled(q) ? 0 : div_u64(wbt_get_min_lat(q), 1000);
> +
> +	return sprintf(page, "%llu\n", lat);
>  }
>  
>  static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
> @@ -493,6 +497,9 @@ static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
>  			return ret;
>  	}
>  
> +	if (wbt_disabled(q))
> +		return -EINVAL;
> +
>  	if (val == -1)
>  		val = wbt_default_latency_nsec(q);
>  	else if (val >= 0)
> diff --git a/block/blk-wbt.c b/block/blk-wbt.c
> index a9982000b667..68851c2c02d2 100644
> --- a/block/blk-wbt.c
> +++ b/block/blk-wbt.c
> @@ -422,6 +422,13 @@ static void wbt_update_limits(struct rq_wb *rwb)
>  	rwb_wake_all(rwb);
>  }
>  
> +bool wbt_disabled(struct request_queue *q)
> +{
> +	struct rq_qos *rqos = wbt_rq_qos(q);
> +
> +	return !rqos || RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT;
> +}
> +
>  u64 wbt_get_min_lat(struct request_queue *q)
>  {
>  	struct rq_qos *rqos = wbt_rq_qos(q);
> diff --git a/block/blk-wbt.h b/block/blk-wbt.h
> index 7e44eccc676d..e42465ddcbb6 100644
> --- a/block/blk-wbt.h
> +++ b/block/blk-wbt.h
> @@ -94,6 +94,7 @@ void wbt_enable_default(struct request_queue *);
>  
>  u64 wbt_get_min_lat(struct request_queue *q);
>  void wbt_set_min_lat(struct request_queue *q, u64 val);
> +bool wbt_disabled(struct request_queue *);
>  
>  void wbt_set_write_cache(struct request_queue *, bool);
>  
> @@ -125,6 +126,10 @@ static inline u64 wbt_default_latency_nsec(struct request_queue *q)
>  {
>  	return 0;
>  }
> +static inline bool wbt_disabled(struct request_queue *q)
> +{
> +	return true;
> +}
>  
>  #endif /* CONFIG_BLK_WBT */
>  
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR