[PATCH v2] Improve the performance of --num-threads -d 31

[min-usui@xxxxxxxxxxxxx (Minoru Usui)]

Hi, Zhou

> >>>>> ===
> >>>>>      producer                   Consumer
> >>>>> ---------------------------------------------------------
> >>>>>      pthread_mutex_lock()
> >>>>>      pfn = info->current_pfn
> >>>>>                                 info->current_pfn = end_pfn
> >>>>>      info->current_pfn++
> >>>>>        -> end_pfn + 1
> >>>>>      pthread_mutex_unlock()
> >>>>> ===
> 
> How about just changing "info->current_pfn = end_pfn" to "info->current_pfn--" ?
> Just like the first version of the patch.

If you don't get mutex lock in consumer side, this change is meaningless.
Of course, info->current_pfn may equal to end_pfn at the end of the cycle,
but there is a timing that info->current_pfn is bigger than end_pfn in processing producer thread.

The root cause is producer increments info->current_pfn everytime, even if info->current_pfn == end_pfn 
in following code.

===
>>>> +			/* get next pfn */
>>>> +			pthread_mutex_lock(&info->current_pfn_mutex);
>>>> +			pfn = info->current_pfn;
>>>> +			info->current_pfn++;                        # increment everytime
>>>> +			page_flag_buf->ready = FLAG_FILLING;
>>>> +			pthread_mutex_unlock(&info->current_pfn_mutex);
>>>>
>>>> -			buf_ready = TRUE;
>>>> +			page_flag_buf->pfn = pfn;
>>>>
>>>> -			page_data_buf[index].pfn = pfn;
>>>> -			page_data_buf[index].ready = 1;
>>>> +			if (pfn >= kdump_thread_args->end_pfn) {
>>>> +				page_data_buf[index].used = FALSE;
>>>> +				page_flag_buf->ready = FLAG_READY;
>>>> +				break;                             # not decrement
>>>> +			}
===

If you don't allow info->current_pfn is bigger than end_pfn,
you don't need to increment info->current_pfn when pfn >= kdump_thread_args->end_pfn like following.

===
                        /* get next pfn */
                        pthread_mutex_lock(&info->current_pfn_mutex);
                        pfn = info->current_pfn;
                        page_flag_buf->pfn = pfn;
                        if (pfn >= kdump_thread_args->end_pfn) {
                                page_data_buf[index].used = FALSE;
                                page_flag_buf->ready = FLAG_READY;
                                pthread_mutex_unlock(&info->current_pfn_mutex);
                                break;
                        }
                        page_flag_buf->ready = FLAG_FILLING;
                        info->current_pfn++;
                        pthread_mutex_unlock(&info->current_pfn_mutex);
===

If you allow info->current_pfn is bigger than end_pfn, producer doesn't need to change info->current_pfn.

---
Thanks
Minoru Usui