linux-kernel - Re: [PATCH 05/11] blk-throttle: simpfy low limit reached check in throtl_tg_can

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Message-ID: <Y35l3cRfYNgCzBgC@slm.duckdns.org>
Date:   Wed, 23 Nov 2022 08:26:37 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Kemeng Shi <shikemeng@...wei.com>
Cc:     josef@...icpanda.com, axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/11] blk-throttle: simpfy low limit reached check in
 throtl_tg_can_upgrade

On Wed, Nov 23, 2022 at 02:03:55PM +0800, Kemeng Shi wrote:
> -static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
> +static bool throtl_tg_reach_low_limit(struct throtl_grp *tg, int rw)
>  {
>  	struct throtl_service_queue *sq = &tg->service_queue;
> -	bool read_limit, write_limit;
> +	bool limit = tg->bps[rw][LIMIT_LOW] || tg->iops[rw][LIMIT_LOW];
>  
>  	/*
>  	 * if cgroup reaches low limit (if low limit is 0, the cgroup always
>  	 * reaches), it's ok to upgrade to next limit
>  	 */
> -	read_limit = tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW];
> -	write_limit = tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW];
> -	if (!read_limit && !write_limit)
> -		return true;
> -	if (read_limit && sq->nr_queued[READ] &&
> -	    (!write_limit || sq->nr_queued[WRITE]))
> -		return true;
> -	if (write_limit && sq->nr_queued[WRITE] &&
> -	    (!read_limit || sq->nr_queued[READ]))
> +	return !limit || sq->nr_queued[rw].
> +}
> +
> +static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
> +{
> +	if (throtl_tg_reach_low_limit(tg, READ) &&
> +	    throtl_tg_reach_low_limit(tg, WRITE))

Are the conditions being checked actually equivalent? If so, can you
explicitly explain that these are equivalent conditions? If not, what are we
changing exactly?

Thanks.

-- 
tejun