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

Alexandra Winter
2023-11-21T15:40:16Z

On 21.11.23 14:41, Yury Norov wrote:
> On Mon, Nov 20, 2023 at 09:43:54AM +0100, Alexandra Winter wrote:
>>
>>
>> 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@gmail.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.
>
> I'll add:
>
> If find_and_set_bit() doesn't acquire a bit, it returns
> ->wr_tx_cnt, and so explicit initialization of *idx with
> the same value is unneeded.
>
> Makes sense?
>

Makes sense for the -EBUSY case, thank you.
It does not explain that you also removed the line for the -ENOLINK case
(which is ok, because the caller has also initialized it to link->wr_tx_cnt)