linux-kernel - Re: [PATCH 1/3] blk-wbt: Optimize wbt

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Message-ID: <k7g33ohjbc7tuo3vzhsdl4qzmbjafxncnvfduxggilmdb53mxc@3y37mw7jqw4z>
Date: Fri, 25 Jul 2025 17:56:21 +0200
From: Jan Kara <jack@...e.cz>
To: Tang Yizhou <yizhou.tang@...pee.com>
Cc: axboe@...nel.dk, hch@....de, jack@...e.cz, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org, tangyeechou@...il.com
Subject: Re: [PATCH 1/3] blk-wbt: Optimize wbt_done() for non-throttled writes

On Thu 24-07-25 16:29:59, Tang Yizhou wrote:
> From: Tang Yizhou <yizhou.tang@...pee.com>
> 
> In the current implementation, the sync_cookie and last_cookie members of
> struct rq_wb are used only by read requests and not by non-throttled write
> requests. Based on this, we can optimize wbt_done() by removing one if
> condition check for non-throttled write requests.
> 
> Signed-off-by: Tang Yizhou <yizhou.tang@...pee.com>

Nah, I'm undecided if this is actually worth it. But it looks correct and
doesn't make the code harder to follow so I guess feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  block/blk-wbt.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/block/blk-wbt.c b/block/blk-wbt.c
> index a50d4cd55f41..30886d44f6cd 100644
> --- a/block/blk-wbt.c
> +++ b/block/blk-wbt.c
> @@ -248,13 +248,14 @@ static void wbt_done(struct rq_qos *rqos, struct request *rq)
>  	struct rq_wb *rwb = RQWB(rqos);
>  
>  	if (!wbt_is_tracked(rq)) {
> -		if (rwb->sync_cookie == rq) {
> -			rwb->sync_issue = 0;
> -			rwb->sync_cookie = NULL;
> -		}
> +		if (wbt_is_read(rq)) {
> +			if (rwb->sync_cookie == rq) {
> +				rwb->sync_issue = 0;
> +				rwb->sync_cookie = NULL;
> +			}
>  
> -		if (wbt_is_read(rq))
>  			wb_timestamp(rwb, &rwb->last_comp);
> +		}
>  	} else {
>  		WARN_ON_ONCE(rq == rwb->sync_cookie);
>  		__wbt_done(rqos, wbt_flags(rq));
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR