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

Atsushi Kumagai ats-kumagai at wm.jp.nec.com
Thu Jan 21 20:53:45 PST 2016


Hello Zhou,

>The origin implementation of --num-threads wastes a lot of time
>dealing with the filtered pages. So it has a great performance degradation
>when -d 31 is specified.
>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.
>It won't waste time and memory for filtered page. So it has a good behaviour in -d 31.
>
>Some tests results:
>
>      -l                                   -c
>-d 31: 2.6                                 11.3 (without num-threads)
>       num-threads    origin    new        origin    new
>       1              13.2      2.9        22.4      13.2
>       2              11.6      2.46       15.3      7.3
>       4              10.4      3.2        12.3      5.7
>-d 0:  32.7                                151.2(without num-threads)
>       1              43.3      45.3       158.9     159.4
>       2              21.2      23.0       81.8      83.2
>       4              18.2      21.4       46.1      47.5
>
>These tests are executed in the second kernel with /proc/vmcore.

I appreciate your work, the effect looks great.
There are still some performance degradation depending on the dump level,
but the problem we discussed is "especially -d31 is too slow",
so I think this patch is enough for now.

BTW, I have some small comments for cleanup, please check below.

>---
> makedumpfile.c | 266 +++++++++++++++++++++++++++++++++++++++------------------
> makedumpfile.h |  26 +++---
> 2 files changed, 196 insertions(+), 96 deletions(-)
>
>diff --git a/makedumpfile.c b/makedumpfile.c
>index fa0b779..8cf274b 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) {
>+			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;
>+			}
>+			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 +7172,48 @@ 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) {
>+		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;
>
> 		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)
>+			/* 1 means page_flag_buf is ready to be used */
>+			if (page_flag_buf->ready == 1)
> 				continue;

For status flag, enum is preferable to explaining a magic number by comment.

>
>-			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++;
>+			/* 2 means page_flag_buf is being filled */
>+			page_flag_buf->ready = 2;
>+			pthread_mutex_unlock(&info->current_pfn_mutex);
>
>-			if (page_data_buf[index].ready != 0)
>-				goto unlock;
>+			page_flag_buf->pfn = 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 = 1;
>+				info->current_pfn--;
>+				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 +7226,11 @@ 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 +7280,16 @@ 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 = 1;
>+			page_flag_buf = page_flag_buf->next;
>
> 		}
>-	}
>
>+		pthread_mutex_unlock(&page_data_buf[index].mutex);
>+	}
> 	retval = NULL;
>
> fail:
>@@ -7265,14 +7317,15 @@ 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 +7372,11 @@ 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 = 0;
> 		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 +7390,9 @@ 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 +7405,101 @@ write_kdump_pages_parallel_cyclic(struct cache_data *cd_header,
> 		}
> 	}
>
>-	consuming_pfn = start_pfn;
>-	index = -1;
>+	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.
>+		 */
>+		/*
>+		 *
>+		 */

I hope such garbage will be removed in the next version.

Thanks,
Atsushi Kumagai

>+		while (1) {
>+			current_pfn = end_pfn;
>+			end_count = 0;
>
>-	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++) {
>
>-		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;
>-		}
>+				/*
>+				 * ready == 0 means the page_flag_buf haven't been used.
>+				 * So we will skip it.
>+				 */
>+				if (info->page_flag_buf[i]->ready == 0)
>+					continue;
>+				temp_pfn = info->page_flag_buf[i]->pfn;
>
>-		/*
>-		 * check pfn first without mutex locked to reduce the time
>-		 * trying to lock the mutex
>-		 */
>-		if (page_data_buf[index].pfn != consuming_pfn)
>-			continue;
>+				/*
>+				 * count how many threads have reached the end.
>+				 */
>+				if (temp_pfn >= end_pfn) {
>+					end_count++;
>+					continue;
>+				}
>
>-		if (pthread_mutex_trylock(&page_data_buf[index].mutex) != 0)
>-			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;
>+
>+			/*
>+			 * When we check the pfn in page_flag_buf, it may be being produced.
>+			 * So we should wait until it is ready to use. And if the pfn is
>+			 * different from the value when we check, we should rechoose the buf.
>+			 */
>+			gettimeofday(&last, NULL);
>+			while (info->page_flag_buf[consuming]->ready != 1) {
>+				gettimeofday(&new, NULL);
>+				if (new.tv_sec - last.tv_sec > WAIT_TIME) {
>+					ERRMSG("Can't get data of pfn.\n");
>+					goto out;
>+				}
>+			}
>+
>+			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 +7515,12 @@ 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 = 0;
> 		}
>-unlock:
>-		pthread_mutex_unlock(&page_data_buf[index].mutex);
>+		info->page_flag_buf[consuming]->ready = 0;
>+		info->page_flag_buf[consuming] = info->page_flag_buf[consuming]->next;
>
> 	}
>-
>+finish:
> 	ret = TRUE;
> 	/*
> 	 * print [100 %]
>@@ -7464,7 +7559,7 @@ 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 +7659,7 @@ 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..7452e24 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 +985,31 @@ struct mmap_cache {
> 	off_t   mmap_end_offset;
> };
>
>+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 +1298,7 @@ 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
>
>
>
>
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