netdev - Re: [PATCH net-next 1/3] net: provide macros for commonly copied lockless queue stop/wake code

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Date:   Thu, 23 Mar 2023 10:23:32 +0530
From:   Pavan Chebbi <pavan.chebbi@...adcom.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
        pabeni@...hat.com, willemb@...gle.com, alexander.duyck@...il.com
Subject: Re: [PATCH net-next 1/3] net: provide macros for commonly copied
 lockless queue stop/wake code

On Thu, Mar 23, 2023 at 5:01 AM Jakub Kicinski <kuba@...nel.org> wrote:
> +
> +#define netif_tx_queue_try_stop(txq, get_desc, start_thrs)             \
> +       ({                                                              \
> +               int _res;                                               \
> +                                                                       \
> +               netif_tx_stop_queue(txq);                               \
> +                                                                       \
> +               smp_mb();                                               \
> +                                                                       \
> +               /* We need to check again in a case another             \
> +                * CPU has just made room available.                    \
> +                */                                                     \
> +               if (likely(get_desc < start_thrs)) {                    \

I am only curious to understand why initializing _res with likely
result and having a condition to cover only the unlikely case, would
not be better.
As in:
    int _res = 0;
    if (unlikely(get_desc >= start_thrs) {
        start_queue()
        _res = -1
    }

> +                       _res = 0;                                       \
> +               } else {                                                \
> +                       netif_tx_start_queue(txq);                      \
> +                       _res = -1;                                      \
> +               }                                                       \
> +               _res;                                                   \
> +       })                                                              \
> +
> --
> 2.39.2
>

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