On Fri, 5 Sep 2025 10:53:37 +0200, Przemek Kitszel wrote:
>
>>>>>> + if (adapter->last_rss_indices != rss_i ||
>>>>>> + adapter->last_reta_entries != reta_entries) {
>>>>>> + for (i = 0; i < reta_entries; i++)
>>>>>> + adapter->rss_indir_tbl[i] = i % rss_i;
>>>>> Are you sure rss_i never ever can be a 0?
>>>>> This is the only thing I'm worrying about.
>>>>
>>>> Oops, you're exactly right. Good catch!
>>>>
>>>> I see the original code assigns 0 to rss_indir_tbl[i] when rss_i is
>>> 0,
>>>> like:
>>>> adapter->rss_indir_tbl[i] = 0;
>>>
>>> Ahh, that's not true, my brain was not working... Sorry for messing
>>> up.
>>> Anyway, in a situation where rss_i == 0, we should handle it somehow
>>> to avoid zero-divisor.
>>>
>>>>
>>>> To handle this with keeping the behavior when rss_i == 0, I'm
>>>> considering Option 1:
>>>> adapter->rss_indir_tbl[i] = rss_i ? i % rss_i : 0;
>>>>
>>>> Option 2:
>>>> if (rss_i)
>>>> for (i = 0; i < reta_entries; i++)
>>>> adapter->rss_indir_tbl[i] = i % rss_i;
>>>> else
>>>> memset(adapter->rss_indir_tbl, 0, reta_entries);
>>>>
>>>> Since this is not in the data path, the overhead of checking rss_i in
>>>> each iteration might be acceptable. Therefore I'd like to adopt the
>>>> option 1 for simplicity.
>>>>
>>>> Do you have any preference or other suggestions?
>>
>> I lean toward option 2, as the explicit if (rss_i) guard makes the logic
>> clearer and easier to follow.
>>
>> Handling the simplified case first with:
>> if (unlikely(!rss_i))
>> memset(adapter->rss_indir_tbl, 0, reta_entries);
>> else
>> for (i = 0; i < reta_entries; i++)
>> adapter->rss_indir_tbl[i] = i % rss_i;
>>
>> Improves readability and separates the edge case from the main logic.
>>
>> While it's possible to use a ternary expression like
>> adapter->rss_indir_tbl[i] = rss_i ? i % rss_i : 0;,
>> I find the conditional block more maintainable, especially if this logic
>> evolves later.
>>
>> Regarding unlikely(), unless there's profiling data showing a performance
>> benefit,
>> I'd avoid it here - this isn't in the fast path, and clarity should take
>> precedence.
>> With the best regards Alex
>
>I would make it even simpler (than if/else paths):
>
>if (!rss_i)
> rss_i = 1;
>
>(which looks better than "should be obvious" oneliner, rss_i += !rss_i;)
>
Sounds good.
Considering comparing adapter->last_rss_indices and rss_i before
configuring rss_indir_tbl and saving rss_i to adapter->last_rss_indices
afterwards, I think I have to do that before the comparison.
Is my understanding correct?
+ if (!rss_i)
+ rss_i = 1;
+
+ if (adapter->last_rss_indices != rss_i ||
+ adapter->last_reta_entries != reta_entries) {
+ for (i = 0; i < reta_entries; i++)
+ adapter->rss_indir_tbl[i] = i % rss_i;
