netdev - Re: [PATCH 29/34] net: smc: fix opencoded find_and_set_bit() in smc_wr_tx_get_free_slot

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Date: Mon, 20 Nov 2023 09:43:54 +0100
From: Alexandra Winter <wintera@...ux.ibm.com>
To: Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org,
        Karsten Graul <kgraul@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>, Jan Karcher <jaka@...ux.ibm.com>,
        "D. Wythe" <alibuda@...ux.alibaba.com>,
        Tony Lu <tonylu@...ux.alibaba.com>, Wen Gu <guwen@...ux.alibaba.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-s390@...r.kernel.org,
        netdev@...r.kernel.org
Cc: Jan Kara <jack@...e.cz>, Mirsad Todorovac
 <mirsad.todorovac@....unizg.hr>,
        Matthew Wilcox <willy@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Alexey Klimov <klimov.linux@...il.com>
Subject: Re: [PATCH 29/34] net: smc: fix opencoded find_and_set_bit() in
 smc_wr_tx_get_free_slot_index()



On 18.11.23 16:51, Yury Norov wrote:
> The function opencodes find_and_set_bit() with a for_each() loop. Fix
> it, and make the whole function a simple almost one-liner.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
>  net/smc/smc_wr.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/net/smc/smc_wr.c b/net/smc/smc_wr.c
> index 0021065a600a..b6f0cfc52788 100644
> --- a/net/smc/smc_wr.c
> +++ b/net/smc/smc_wr.c
> @@ -170,15 +170,11 @@ void smc_wr_tx_cq_handler(struct ib_cq *ib_cq, void *cq_context)
>  
>  static inline int smc_wr_tx_get_free_slot_index(struct smc_link *link, u32 *idx)
>  {
> -	*idx = link->wr_tx_cnt;
>  	if (!smc_link_sendable(link))
>  		return -ENOLINK;
> -	for_each_clear_bit(*idx, link->wr_tx_mask, link->wr_tx_cnt) {
> -		if (!test_and_set_bit(*idx, link->wr_tx_mask))
> -			return 0;
> -	}
> -	*idx = link->wr_tx_cnt;
> -	return -EBUSY;
> +
> +	*idx = find_and_set_bit(link->wr_tx_mask, link->wr_tx_cnt);
> +	return *idx < link->wr_tx_cnt ? 0 : -EBUSY;
>  }
>  
>  /**


My understanding is that you can omit the lines with
> -	*idx = link->wr_tx_cnt;
because they only apply to the error paths and you checked that the calling function
does not use the idx variable in the error cases. Do I understand this correct?

If so the removal of these 2 lines is not related to your change of using find_and_set_bit(),
do I understand that correctly?

If so, it may be worth mentioning that in the commit message.