On 4/26/23 7:41?PM, Jens Axboe wrote:
>> +static void io_napi_multi_busy_loop(struct list_head *napi_list,
>> + struct io_wait_queue *iowq)
>> +{
>> + unsigned long start_time = busy_loop_current_time();
>> +
>> + do {
>> + if (list_is_singular(napi_list))
>> + break;
>> + if (!__io_napi_busy_loop(napi_list, iowq->napi_prefer_busy_poll))
>> + break;
>> + } while (!io_napi_busy_loop_should_end(iowq, start_time));
>> +}
>
> Do we need to check for an empty list here?
>
>> +static void io_napi_blocking_busy_loop(struct list_head *napi_list,
>> + struct io_wait_queue *iowq)
>> +{
>> + if (!list_is_singular(napi_list))
>> + io_napi_multi_busy_loop(napi_list, iowq);
>> +
>> + if (list_is_singular(napi_list)) {
>> + struct io_napi_ht_entry *ne;
>> +
>> + ne = list_first_entry(napi_list, struct io_napi_ht_entry, list);
>> + napi_busy_loop(ne->napi_id, io_napi_busy_loop_should_end, iowq,
>> + iowq->napi_prefer_busy_poll, BUSY_POLL_BUDGET);
>> + }
>> +}
>
> Presumably io_napi_multi_busy_loop() can change the state of the list,
> which is why we have if (cond) and then if (!cond) here? Would probably
> warrant a comment as it looks a bit confusing.
Doesn't look like that's the case? We just call into
io_napi_multi_busy_loop() -> napi_busy_loop() which doesn't touch it. So
the state should be the same?
We also check if the list isn't singular before we call it, and then
io_napi_multi_busy_loop() breaks out of the loop if it is. And we know
it's not singular when calling, and I don't see what changes it.
Unless I'm missing something, which is quite possible, this looks overly
convoluted and has extra pointless checks?
--
Jens Axboe
