lkml.org 
[lkml]   [2022]   [Apr]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH -next RFC v2 8/8] sbitmap: wake up the number of threads based on required tags
From
Date
在 2022/04/09 5:13, Bart Van Assche 写道:
> On 4/8/22 00:39, Yu Kuai wrote:
>> +static unsigned int get_wake_nr(struct sbq_wait_state *ws, unsigned
>> int nr_tags)
>> +{
>> +    struct sbq_wait *wait;
>> +    struct wait_queue_entry *entry;
>> +    unsigned int nr = 1;
>> +
>> +    spin_lock_irq(&ws->wait.lock);
>> +    list_for_each_entry(entry, &ws->wait.head, entry) {
>> +        wait = container_of(entry, struct sbq_wait, wait);
>> +        if (nr_tags <= wait->nr_tags)
>> +            break;
>> +
>> +        nr++;
>> +        nr_tags -= wait->nr_tags;
>> +    }
>> +    spin_unlock_irq(&ws->wait.lock);
>> +
>> +    return nr;
>> +}
>> +
>>   static bool __sbq_wake_up(struct sbitmap_queue *sbq)
>>   {
>>       struct sbq_wait_state *ws;
>> @@ -648,7 +668,7 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
>>       smp_mb__before_atomic();
>>       atomic_set(&ws->wait_cnt, wake_batch);
>>       sbq_update_preemption(sbq, wake_batch);
>> -    wake_up_nr(&ws->wait, wake_batch);
>> +    wake_up_nr(&ws->wait, get_wake_nr(ws, wake_batch));
>>       return true;
>>   }
>
> An additional comment: my understanding is that __sbq_wake_up() should
> wake up exactly `wake_batch` waiters. The above patch changes that into
> waking up at most `wake_batch` waiters. I think that's wrong.
Hi,

I think the reason to wake up 'wake_batch' waiters is to make sure
wakers will use up 'wake_batch' tags that is just freed, because each
wakers should aquire at least one tag. Thus I think if we can make sure
wakers will use up 'wake_batch' tags, it's ok to wake up less waiters.

Please kindly correct me if I'm wrong.

Thanks,
Kuai
>
> Bart.
> .
>

\
 
 \ /
  Last update: 2022-04-09 04:18    [W:0.158 / U:0.376 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site