Re: [PATCH v1] Improve the performance of --num-threads -d 31

["\"Zhou, Wenjian/周文剑\"" <zhouwj-fnst@cn.fujitsu.com>]

On 02/15/2016 10:15 AM, "Zhou, Wenjian/周文剑" wrote:
> Hello Usui,
>
> Thanks very much for your comments.
> And sorry for the late reply.
>
> See below.
>
> On 02/08/2016 01:00 PM, Minoru Usui wrote:
>> Hello,
>>
>>> -----Original Message-----
>>> From: kexec [mailto:kexec-bounces@lists.infradead.org] On Behalf Of Minoru Usui
>>> Sent: Thursday, February 04, 2016 8:52 AM
>>> To: Zhou Wenjian <zhouwj-fnst@cn.fujitsu.com>; kexec@lists.infradead.org
>>> Subject: Re: [PATCH v1] Improve the performance of --num-threads -d 31
>>>
>>> Hi, Zhou
>>>
>>> I have some comments.
>>> I'm sorry if I have misunderstood your code.
>>>
>>>> -----Original Message-----
>>>> From: kexec [mailto:kexec-bounces@lists.infradead.org] On Behalf Of Zhou Wenjian
>>>> Sent: Monday, February 01, 2016 3:22 PM
>>>> To: kexec@lists.infradead.org
>>>> Subject: [PATCH v1] Improve the performance of --num-threads -d 31
>>>>
>>>> v1:
>>>>          1. change page_flag.ready's value to enum
>>>>          2. change the patch description
>>>>          3. cleanup some codes
>>>>     4. fix a bug in cyclic mode
>>>>
>>>> multi-threads implementation will introduce extra cost when handling
>>>> each page. The origin implementation will also do the extra work for
>>>> filtered pages. So there is a big performance degradation in
>>>> --num-threads -d 31.
>>>> The new implementation won't do the extra work for filtered pages any
>>>> more. So the performance of -d 31 is close to that of serial processing.
>>>>
>>>> The new implementation is just like the following:
>>>>          * The basic idea is producer producing page and consumer writing page.
>>>>          * Each producer have a page_flag_buf list which is used for storing
>>>>            page's description.
>>>>          * The size of page_flag_buf is little so it won't take too much memory.
>>>>          * And all producers will share a page_data_buf array which is
>>>>            used for storing page's compressed data.
>>>>          * The main thread is the consumer. It will find the next pfn and write
>>>>            it into file.
>>>>          * The next pfn is smallest pfn in all page_flag_buf.
>>>>
>>>> Signed-off-by: Zhou Wenjian <zhouwj-fnst@cn.fujitsu.com>
>>>> ---
>>>>   makedumpfile.c | 258 ++++++++++++++++++++++++++++++++++++++-------------------
>>>>   makedumpfile.h |  31 ++++---
>>>>   2 files changed, 193 insertions(+), 96 deletions(-)
>>>>
>>>> diff --git a/makedumpfile.c b/makedumpfile.c
>>>> index fa0b779..0ecd065 100644
>>>> --- a/makedumpfile.c
>>>> +++ b/makedumpfile.c
>>>> @@ -3483,7 +3483,8 @@ initial_for_parallel()
>>>>       unsigned long page_data_buf_size;
>>>>       unsigned long limit_size;
>>>>       int page_data_num;
>>>> -    int i;
>>>> +    struct page_flag *current;
>>>> +    int i, j;
>>>>
>>>>       len_buf_out = calculate_len_buf_out(info->page_size);
>>>>
>>>> @@ -3562,8 +3563,10 @@ initial_for_parallel()
>>>>                 - MAP_REGION * info->num_threads) * 0.6;
>>>>
>>>>       page_data_num = limit_size / page_data_buf_size;
>>>> +    info->num_buffers = 3 * info->num_threads;
>>>>
>>>> -    info->num_buffers = MIN(NUM_BUFFERS, page_data_num);
>>>> +    info->num_buffers = MAX(info->num_buffers, NUM_BUFFERS);
>>>> +    info->num_buffers = MIN(info->num_buffers, page_data_num);
>>>>
>>>>       DEBUG_MSG("Number of struct page_data for produce/consume: %d\n",
>>>>               info->num_buffers);
>>>> @@ -3588,6 +3591,36 @@ initial_for_parallel()
>>>>       }
>>>>
>>>>       /*
>>>> +     * initial page_flag for each thread
>>>> +     */
>>>> +    if ((info->page_flag_buf = malloc(sizeof(void *) * info->num_threads))
>>>> +        == NULL) {
>>>> +        MSG("Can't allocate memory for page_flag_buf. %s\n",
>>>> +                strerror(errno));
>>>> +        return FALSE;
>>>> +    }
>>>> +    memset(info->page_flag_buf, 0, sizeof(void *) * info->num_threads);
>>>> +
>>>> +    for (i = 0; i < info->num_threads; i++) {
>>>> +        if ((info->page_flag_buf[i] = malloc(sizeof(struct page_flag))) == NULL) {
>>>
>>> Fist element of struct page_flag in circular list is allocated by malloc(),
>>> but other elements are allocated by calloc().(see below)
>>> I think both elements should be allocated by calloc().
>>>
>
> Yes, you are right.
> I have made a mistake.
>
>>>> +            MSG("Can't allocate memory for page_flag_buf. %s\n",
>>>> +                strerror(errno));
>>>> +            return FALSE;
>>>> +        }
>>>> +        current = info->page_flag_buf[i];
>>>> +
>>>> +        for (j = 1; j < NUM_BUFFERS; j++) {
>>>> +            if ((current->next = calloc(0, sizeof(struct page_flag))) == NULL) {
>>>> +                MSG("Can't allocate memory for data of page_data_buf. %s\n",
>>>> +                    strerror(errno));
>>>> +                return FALSE;
>>>> +            }
>>>
>>>
>>> First argument of calloc() should be 1, not 0.
>>> And there is typo in error message.
>>> Allocated element is not page_data_buf.
>>>
>
> I agree.
>
>>>> +            current = current->next;
>>>> +        }
>>>> +        current->next = info->page_flag_buf[i];
>>>> +    }
>>>> +
>>>> +    /*
>>>>        * initial fd_memory for threads
>>>>        */
>>>>       for (i = 0; i < info->num_threads; i++) {
>>>> @@ -3612,7 +3645,8 @@ initial_for_parallel()
>>>>   void
>>>>   free_for_parallel()
>>>>   {
>>>> -    int i;
>>>> +    int i, j;
>>>> +    struct page_flag *current;
>>>>
>>>>       if (info->threads != NULL) {
>>>>           for (i = 0; i < info->num_threads; i++) {
>>>> @@ -3655,6 +3689,19 @@ free_for_parallel()
>>>>           free(info->page_data_buf);
>>>>       }
>>>>
>>>> +    if (info->page_flag_buf != NULL) {
>>>> +        for (i = 0; i < info->num_threads; i++) {
>>>> +            for (j = 0; j < NUM_BUFFERS; j++) {
>>>> +                if (info->page_flag_buf[i] != NULL) {
>>>> +                    current = info->page_flag_buf[i];
>>>> +                    info->page_flag_buf[i] = current->next;
>>>> +                    free(current);
>>>> +                }
>>>> +            }
>>>> +        }
>>>> +        free(info->page_flag_buf);
>>>> +    }
>>>> +
>>>>       if (info->parallel_info == NULL)
>>>>           return;
>>>>
>>>> @@ -7076,10 +7123,10 @@ kdump_thread_function_cyclic(void *arg) {
>>>>       void *retval = PTHREAD_FAIL;
>>>>       struct thread_args *kdump_thread_args = (struct thread_args *)arg;
>>>>       struct page_data *page_data_buf = kdump_thread_args->page_data_buf;
>>>> +    struct page_flag *page_flag_buf = kdump_thread_args->page_flag_buf;
>>>>       struct cycle *cycle = kdump_thread_args->cycle;
>>>> -    int page_data_num = kdump_thread_args->page_data_num;
>>>>       mdf_pfn_t pfn;
>>>> -    int index;
>>>> +    int index = kdump_thread_args->thread_num;
>>>>       int buf_ready;
>>>>       int dumpable;
>>>>       int fd_memory = 0;
>>>> @@ -7125,47 +7172,47 @@ kdump_thread_function_cyclic(void *arg) {
>>>>                           kdump_thread_args->thread_num);
>>>>       }
>>>>
>>>> -    while (1) {
>>>> -        /* get next pfn */
>>>> -        pthread_mutex_lock(&info->current_pfn_mutex);
>>>> -        pfn = info->current_pfn;
>>>> -        info->current_pfn++;
>>>> -        pthread_mutex_unlock(&info->current_pfn_mutex);
>>>> +    /*
>>>> +     * filtered page won't take anything
>>>> +     * unfiltered zero page will only take a page_flag_buf
>>>> +     * unfiltered non-zero page will take a page_flag_buf and a page_data_buf
>>>> +     */
>>>> +    while (page_flag_buf->pfn < kdump_thread_args->end_pfn) {
>>>
>>> At first, page_flag_buf->pfn is not initialized.
>>> I think this block should be replaced with the following code.
>>>
>>> ===
>>>    do {
>>>      :
>>>    } while(page_flag_buf->pfn < kdump_thread_args->end_pfn)
>>> ===
>>
>> I'm sorry, above suggestion is meaningless in terms of page_flag_buf->pfn is uninitialized.
>> It should be replaced like following.
>>
>> ===
>>    while (1) {
>>      :
>>      while (buf_ready == FALSE) {
>>         :
>>        if (pfn >= kdump_thread_args->end_pfn) {
>>           :
>>          goto finish;
>>        }
>>        :
>>      }
>>      :
>>    }
>> finish:
>> ===
>>
>
> page_flag_buf is allocated by calloc().
> The page_flag_buf->pfn's value is 0.
> So I think it is not necessary to modify the code.
>
>> Thanks,
>> Minoru Usui
>>
>>
>>>> +        buf_ready = FALSE;
>>>>
>>>> -        if (pfn >= kdump_thread_args->end_pfn)
>>>> -            break;
>>>> +        while (page_data_buf[index].used != 0 ||
>>>> +                pthread_mutex_trylock(&page_data_buf[index].mutex) != 0)
>>>> +            index = (index + 1) % info->num_buffers;
>>>>
>>>> -        index = -1;
>>>> -        buf_ready = FALSE;
>>>> +        page_data_buf[index].used = 1;
>>>
>>> "1" is a magic number.
>>> It should be changed TRUE or FALSE.
>>>
>
> I see.
>
>>>>           while (buf_ready == FALSE) {
>>>>               pthread_testcancel();
>>>> -
>>>> -            index = pfn % page_data_num;
>>>> -
>>>> -            if (pfn - info->consumed_pfn > info->num_buffers)
>>>> +            if (page_flag_buf->ready == FLAG_READY)
>>>>                   continue;
>>>
>>> At first, page_flag_buf->ready is uninitialized, too.
>>> Should it be initialized in head part of this function, even if FLAG_UNUSED is defined 0?
>>>
>>>
>
> The same topic as the page_flag_buf is allocated by calloc().
>
>>>>
>>>> -            if (page_data_buf[index].ready != 0)
>>>> -                continue;
>>>> -
>>>> -            pthread_mutex_lock(&page_data_buf[index].mutex);
>>>> +            /* get next pfn */
>>>> +            pthread_mutex_lock(&info->current_pfn_mutex);
>>>> +            pfn = info->current_pfn;
>>>> +            info->current_pfn++;
>>>> +            page_flag_buf->ready = FLAG_FILLING;
>>>> +            pthread_mutex_unlock(&info->current_pfn_mutex);
>>>>
>>>> -            if (page_data_buf[index].ready != 0)
>>>> -                goto unlock;
>>>> +            page_flag_buf->pfn = pfn;
>>>
>>> It set FLAG_FILLING to page_flag_buf->ready before setting pfn to page_flag_buf->pfn.
>>> But consumer gets page_flag_buf->pfn after checking page_flag_buf->ready != FLAG_UNUSED
>>> in getting minimum pfn of each thread block.
>>> Should it set page_flag_buf->pfn first?
>>>
>
> Have you noticed the following code in the consumer?
> <cut>
>                          if (current_pfn == info->page_flag_buf[consuming]->pfn)
>                                  break;
> <cut>
>
> The consumer will check if the pfn is changed after the page_flag_buf->ready turns to be FLAG_READY.
> So it's not important whether setting page_flag_buf->pfn first or not.
>
> In the other hand, even setting page_flag_buf->pfn first, if the pfn is not dumpable, the producer
> will also reset the page_flag_buf->pfn.
>
>>>>
>>>> -            buf_ready = TRUE;
>>>> -
>>>> -            page_data_buf[index].pfn = pfn;
>>>> -            page_data_buf[index].ready = 1;
>>>> +            if (pfn >= kdump_thread_args->end_pfn) {
>>>> +                page_data_buf[index].used = 0;
>>>> +                page_flag_buf->ready = FLAG_READY;
>>>> +                info->current_pfn--;
>>>> +                break;
>>>> +            }
>>>
>>> This block decrements info->current_pfn without info->current_pfn_mutex.
>>> I think this block should be moved into previous pthread_mutex_lock(info->current_pfn_mutex) block, so it can remove.
>>>
>
> Why do you think it should have current_pfn_mutex?
>
> If pfn >= kdump_thread_args->end_pfn, info->current_pfn will always larger than
> kdump_thread_args->end_pfn. info->current_pfn-- won't affect anything.
>
> The decrement operation is for cyclic mode.
>

Sorry, it seems I was wrong.
It can't work well in cyclic mode.
I will fix it in the next version.

-- 
Thanks
Zhou




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