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

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

Hello Usui,

On 02/23/2016 09:32 AM, Minoru Usui wrote:
> Hello, Zhou
> 
> Thank you for reflecting my comments.
> I have other comments.
> 
> See below.
> 
>> -----Original Message-----
>> From: kexec [mailto:kexec-bounces@lists.infradead.org] On Behalf Of Zhou Wenjian
>> Sent: Wednesday, February 17, 2016 4:06 PM
>> To: kexec@lists.infradead.org
>> Subject: [PATCH v2] Improve the performance of --num-threads -d 31
>>
>> v2:
>>          1. address Minoru Usui's comments about magic number and error message
>>          2. fix a bug in cyclic mode caused by optimizing
>>
>> 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 | 266 ++++++++++++++++++++++++++++++++++++++-------------------
>>   makedumpfile.h |  31 ++++---
>>   2 files changed, 200 insertions(+), 97 deletions(-)
>>
>> diff --git a/makedumpfile.c b/makedumpfile.c
>> index fa0b779..31329b5 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] = calloc(1, sizeof(struct page_flag))) == NULL) {
>> +			MSG("Can't allocate memory for page_flag. %s\n",
>> +				strerror(errno));
>> +			return FALSE;
>> +		}
>> +		current = info->page_flag_buf[i];
>> +
>> +		for (j = 1; j < NUM_BUFFERS; j++) {
>> +			if ((current->next = calloc(1, sizeof(struct page_flag))) == NULL) {
>> +				MSG("Can't allocate memory for page_flag. %s\n",
>> +					strerror(errno));
>> +				return FALSE;
>> +			}
>> +			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;
>> +	mdf_pfn_t pfn = cycle->start_pfn;
>> +	int index = kdump_thread_args->thread_num;
>>   	int buf_ready;
>>   	int dumpable;
>>   	int fd_memory = 0;
>> @@ -7125,47 +7172,46 @@ 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 (pfn < kdump_thread_args->end_pfn) {
>> +		buf_ready = FALSE;
>>
>> -		if (pfn >= kdump_thread_args->end_pfn)
>> -			break;
>> +		while (page_data_buf[index].used != FALSE ||
>> +				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 = TRUE;
>>
>>   		while (buf_ready == FALSE) {
>>   			pthread_testcancel();
>> -
>> -			index = pfn % page_data_num;
>> -
>> -			if (pfn - info->consumed_pfn > info->num_buffers)
>> -				continue;
>> -
>> -			if (page_data_buf[index].ready != 0)
>> +			if (page_flag_buf->ready == FLAG_READY)
>>   				continue;
>>
>> -			pthread_mutex_lock(&page_data_buf[index].mutex);
>> -
>> -			if (page_data_buf[index].ready != 0)
>> -				goto unlock;
>> +			/* 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);
>>
>> -			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;
>> +			}
>>
>>   			dumpable = is_dumpable(
>>   				info->fd_bitmap ? &bitmap_parallel : info->bitmap2,
>>   				pfn,
>>   				cycle);
>> -			page_data_buf[index].dumpable = dumpable;
>>   			if (!dumpable)
>> -				goto unlock;
>> +				continue;
>>
>>   			if (!read_pfn_parallel(fd_memory, pfn, buf,
>>   					       &bitmap_memory_parallel,
>> @@ -7178,11 +7224,11 @@ kdump_thread_function_cyclic(void *arg) {
>>
>>   			if ((info->dump_level & DL_EXCLUDE_ZERO)
>>   			    && is_zero_page(buf, info->page_size)) {
>> -				page_data_buf[index].zero = TRUE;
>> -				goto unlock;
>> +				page_flag_buf->zero = TRUE;
>> +				goto next;
>>   			}
>>
>> -			page_data_buf[index].zero = FALSE;
>> +			page_flag_buf->zero = FALSE;
>>
>>   			/*
>>   			 * Compress the page data.
>> @@ -7232,12 +7278,16 @@ kdump_thread_function_cyclic(void *arg) {
>>   				page_data_buf[index].size  = info->page_size;
>>   				memcpy(page_data_buf[index].buf, buf, info->page_size);
>>   			}
>> -unlock:
>> -			pthread_mutex_unlock(&page_data_buf[index].mutex);
>> +			page_flag_buf->index = index;
>> +			buf_ready = TRUE;
>> +next:
>> +			page_flag_buf->ready = FLAG_READY;
>> +			page_flag_buf = page_flag_buf->next;
>>
>>   		}
>> -	}
>>
>> +		pthread_mutex_unlock(&page_data_buf[index].mutex);
>> +	}
>>   	retval = NULL;
>>
>>   fail:
>> @@ -7265,14 +7315,15 @@ write_kdump_pages_parallel_cyclic(struct cache_data *cd_header,
>>   	struct page_desc pd;
>>   	struct timeval tv_start;
>>   	struct timeval last, new;
>> -	unsigned long long consuming_pfn;
>>   	pthread_t **threads = NULL;
>>   	struct thread_args *kdump_thread_args = NULL;
>>   	void *thread_result;
>> -	int page_data_num;
>> +	int page_buf_num;
>>   	struct page_data *page_data_buf = NULL;
>>   	int i;
>>   	int index;
>> +	int end_count, consuming, check_count;
>> +	mdf_pfn_t current_pfn, temp_pfn;
>>
>>   	if (info->flag_elf_dumpfile)
>>   		return FALSE;
>> @@ -7319,16 +7370,11 @@ write_kdump_pages_parallel_cyclic(struct cache_data *cd_header,
>>   	threads = info->threads;
>>   	kdump_thread_args = info->kdump_thread_args;
>>
>> -	page_data_num = info->num_buffers;
>> +	page_buf_num = info->num_buffers;
>>   	page_data_buf = info->page_data_buf;
>>
>> -	for (i = 0; i < page_data_num; i++) {
>> -		/*
>> -		 * producer will use pfn in page_data_buf to decide the
>> -		 * consumed pfn
>> -		 */
>> -		page_data_buf[i].pfn = start_pfn - 1;
>> -		page_data_buf[i].ready = 0;
>> +	for (i = 0; i < page_buf_num; i++) {
>> +		page_data_buf[i].used = FALSE;
>>   		res = pthread_mutex_init(&page_data_buf[i].mutex, NULL);
>>   		if (res != 0) {
>>   			ERRMSG("Can't initialize mutex of page_data_buf. %s\n",
>> @@ -7342,8 +7388,9 @@ write_kdump_pages_parallel_cyclic(struct cache_data *cd_header,
>>   		kdump_thread_args[i].len_buf_out = len_buf_out;
>>   		kdump_thread_args[i].start_pfn = start_pfn;
>>   		kdump_thread_args[i].end_pfn = end_pfn;
>> -		kdump_thread_args[i].page_data_num = page_data_num;
>> +		kdump_thread_args[i].page_buf_num = page_buf_num;
>>   		kdump_thread_args[i].page_data_buf = page_data_buf;
>> +		kdump_thread_args[i].page_flag_buf = info->page_flag_buf[i];
>>   		kdump_thread_args[i].cycle = cycle;
>>
>>   		res = pthread_create(threads[i], NULL,
>> @@ -7356,55 +7403,101 @@ write_kdump_pages_parallel_cyclic(struct cache_data *cd_header,
>>   		}
>>   	}
>>
>> -	consuming_pfn = start_pfn;
>> -	index = -1;
>> +	end_count = 0;
>> +	while (1) {
>> +		consuming = 0;
>> +		check_count = 0;
>>
>> -	gettimeofday(&last, NULL);
>> +		/*
>> +		 * 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.
>> +		 */
>> +		gettimeofday(&last, NULL);
>> +		while (1) {
>> +			current_pfn = end_pfn;
>>
>> -	while (consuming_pfn < end_pfn) {
>> -		index = consuming_pfn % page_data_num;
>> +			/*
>> +			 * page_flag_buf is in circular linked list.
>> +			 * The array info->page_flag_buf[] records the current page_flag_buf in each thread's
>> +			 * page_flag_buf list.
>> +			 * consuming is used for recording in which thread the pfn is the smallest.
>> +			 * current_pfn is used for recording the value of pfn when checking the pfn.
>> +			 */
>> +			for (i = 0; i < info->num_threads; i++) {
>> +				if (info->page_flag_buf[i]->ready == FLAG_UNUSED)
>> +					continue;
>> +				temp_pfn = info->page_flag_buf[i]->pfn;
>>
>> -		gettimeofday(&new, NULL);
>> -		if (new.tv_sec - last.tv_sec > WAIT_TIME) {
>> -			ERRMSG("Can't get data of pfn %llx.\n", consuming_pfn);
>> -			goto out;
>> -		}
>> +				/*
>> +				 * count how many threads have reached the end.
>> +				 */
>> +				if (temp_pfn >= end_pfn) {
>> +					/*
>> +					 * prevent setting FLAG_UNUSED being optimized.
>> +					 */
>> +					MSG("-");
> 
> Why does this line need?
> Please clarify why FLAG_UNUSED is optimized.
> 

I tried but still can't figure out the reason or get better solution.
I will be so happy if you can help me.

In gdb, I run it by step.
The code "info->page_flag_buf[i]->ready = FLAG_UNUSED;" can never be reached.
If a breakpoint is set here, the code will never be skipped.

>>
>> -		/*
>> -		 * check pfn first without mutex locked to reduce the time
>> -		 * trying to lock the mutex
>> -		 */
>> -		if (page_data_buf[index].pfn != consuming_pfn)
>> -			continue;
>> +					info->page_flag_buf[i]->ready = FLAG_UNUSED;
>>
>> -		if (pthread_mutex_trylock(&page_data_buf[index].mutex) != 0)
>> -			continue;
>> +					info->current_pfn = end_pfn;
> 
> This part doesn't get info->current_pfn_mutex.
> It becomes bigger than end_pfn at the end of producer thread in following case.
> 
> ===
>    producer                   Consumer
> ---------------------------------------------------------
>    pthread_mutex_lock()
>    pfn = info->current_pfn
>                               info->current_pfn = end_pfn
>    info->current_pfn++
>      -> end_pfn + 1
>    pthread_mutex_unlock()
> ===
> 
> But I know, if this race is happened, processing other producer thread and consumer thread works well
> in current cycle.
> Because each thread checks whether info->current_pfn >= end_pfn.
> 
> On the other hand, info->current_pfn is initialized to cycle->start_pfn before pthread_create()
> in write_kdump_pages_parallel_cyclic().
> This means it does not cause a problem in next cycle, too.
> 
> In other words, my point is following.
> 
>    a) When info->current_pfn changes, you have to get info->current_pfn_mutex.
>    b) If you allow info->current_pfn is bigger than end_pfn at the end of each cycle,
>       "info->current_pfn = end_pfn;" is unnecessary.
> 
> Honestly, I don't like approach b).

You're right. Some thing I thought is wrong.
But I don't like lock if I have other choice.
I will set info->current_pfn before returning.
How about it?

-- 
Thanks
Zhou

> 
> Thanks,
> Minoru Usui
> 
>> +					end_count++;
>> +					continue;
>> +				}
>> +
>> +				if (current_pfn < temp_pfn)
>> +					continue;
>>
>> -		/* check whether the found one is ready to be consumed */
>> -		if (page_data_buf[index].pfn != consuming_pfn ||
>> -		    page_data_buf[index].ready != 1) {
>> -			goto unlock;
>> +				check_count++;
>> +				consuming = i;
>> +				current_pfn = temp_pfn;
>> +			}
>> +
>> +			/*
>> +			 * If all the threads have reached the end, we will finish writing.
>> +			 */
>> +			if (end_count >= info->num_threads)
>> +				goto finish;
>> +
>> +			/*
>> +			 * Since it has the probabilty that there is no page_flag_buf being ready,
>> +			 * we should recheck if it happens.
>> +			 */
>> +			if (check_count == 0)
>> +				continue;
>> +
>> +			/*
>> +			 * If the page_flag_buf is not ready, the pfn recorded may be changed.
>> +			 * So we should recheck.
>> +			 */
>> +			if (info->page_flag_buf[consuming]->ready != FLAG_READY) {
>> +				gettimeofday(&new, NULL);
>> +				if (new.tv_sec - last.tv_sec > WAIT_TIME) {
>> +					ERRMSG("Can't get data of pfn.\n");
>> +					goto out;
>> +				}
>> +				continue;
>> +			}
>> +
>> +			if (current_pfn == info->page_flag_buf[consuming]->pfn)
>> +				break;
>>   		}
>>
>>   		if ((num_dumped % per) == 0)
>>   			print_progress(PROGRESS_COPY, num_dumped, info->num_dumpable);
>>
>> -		/* next pfn is found, refresh last here */
>> -		last = new;
>> -		consuming_pfn++;
>> -		info->consumed_pfn++;
>> -		page_data_buf[index].ready = 0;
>> -
>> -		if (page_data_buf[index].dumpable == FALSE)
>> -			goto unlock;
>> -
>>   		num_dumped++;
>>
>> -		if (page_data_buf[index].zero == TRUE) {
>> +
>> +		if (info->page_flag_buf[consuming]->zero == TRUE) {
>>   			if (!write_cache(cd_header, pd_zero, sizeof(page_desc_t)))
>>   				goto out;
>>   			pfn_zero++;
>>   		} else {
>> +			index = info->page_flag_buf[consuming]->index;
>>   			pd.flags      = page_data_buf[index].flags;
>>   			pd.size       = page_data_buf[index].size;
>>   			pd.page_flags = 0;
>> @@ -7420,12 +7513,12 @@ write_kdump_pages_parallel_cyclic(struct cache_data *cd_header,
>>   			 */
>>   			if (!write_cache(cd_page, page_data_buf[index].buf, pd.size))
>>   				goto out;
>> -
>> +			page_data_buf[index].used = FALSE;
>>   		}
>> -unlock:
>> -		pthread_mutex_unlock(&page_data_buf[index].mutex);
>> +		info->page_flag_buf[consuming]->ready = FLAG_UNUSED;
>> +		info->page_flag_buf[consuming] = info->page_flag_buf[consuming]->next;
>>   	}
>> -
>> +finish:
>>   	ret = TRUE;
>>   	/*
>>   	 * print [100 %]
>> @@ -7464,7 +7557,7 @@ out:
>>   	}
>>
>>   	if (page_data_buf != NULL) {
>> -		for (i = 0; i < page_data_num; i++) {
>> +		for (i = 0; i < page_buf_num; i++) {
>>   			pthread_mutex_destroy(&page_data_buf[i].mutex);
>>   		}
>>   	}
>> @@ -7564,6 +7657,7 @@ write_kdump_pages_cyclic(struct cache_data *cd_header, struct cache_data *cd_pag
>>   		num_dumped++;
>>   		if (!read_pfn(pfn, buf))
>>   			goto out;
>> +
>>   		filter_data_buffer(buf, pfn_to_paddr(pfn), info->page_size);
>>
>>   		/*
>> diff --git a/makedumpfile.h b/makedumpfile.h
>> index e0b5bbf..8a9a5b2 100644
>> --- a/makedumpfile.h
>> +++ b/makedumpfile.h
>> @@ -977,7 +977,7 @@ typedef unsigned long long int ulonglong;
>>   #define PAGE_DATA_NUM	(50)
>>   #define WAIT_TIME	(60 * 10)
>>   #define PTHREAD_FAIL	((void *)-2)
>> -#define NUM_BUFFERS	(50)
>> +#define NUM_BUFFERS	(20)
>>
>>   struct mmap_cache {
>>   	char	*mmap_buf;
>> @@ -985,28 +985,36 @@ struct mmap_cache {
>>   	off_t   mmap_end_offset;
>>   };
>>
>> +enum {
>> +	FLAG_UNUSED,
>> +	FLAG_READY,
>> +	FLAG_FILLING
>> +};
>> +struct page_flag {
>> +	mdf_pfn_t pfn;
>> +	char zero;
>> +	char ready;
>> +	short index;
>> +	struct page_flag *next;
>> +};
>> +
>>   struct page_data
>>   {
>> -	mdf_pfn_t pfn;
>> -	int dumpable;
>> -	int zero;
>> -	unsigned int flags;
>> +	pthread_mutex_t mutex;
>>   	long size;
>>   	unsigned char *buf;
>> -	pthread_mutex_t mutex;
>> -	/*
>> -	 * whether the page_data is ready to be consumed
>> -	 */
>> -	int ready;
>> +	int flags;
>> +	int used;
>>   };
>>
>>   struct thread_args {
>>   	int thread_num;
>>   	unsigned long len_buf_out;
>>   	mdf_pfn_t start_pfn, end_pfn;
>> -	int page_data_num;
>> +	int page_buf_num;
>>   	struct cycle *cycle;
>>   	struct page_data *page_data_buf;
>> +	struct page_flag *page_flag_buf;
>>   };
>>
>>   /*
>> @@ -1295,6 +1303,7 @@ struct DumpInfo {
>>   	pthread_t **threads;
>>   	struct thread_args *kdump_thread_args;
>>   	struct page_data *page_data_buf;
>> +	struct page_flag **page_flag_buf;
>>   	pthread_rwlock_t usemmap_rwlock;
>>   	mdf_pfn_t current_pfn;
>>   	pthread_mutex_t current_pfn_mutex;
>> --
>> 1.8.3.1
>>
>>
>>
>>
>> _______________________________________________
>> kexec mailing list
>> kexec@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/kexec




_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec