[commtech] BatchQueue v2

Uses 2 mapping to the same structure to avoid prefetching of the
producer semi-buffer by the consumer. The idea is to access everything
through mapping 1 except semi-buffer 2 which is accessed through mapping
2.

communication_techniques/Makefile

@@ -14,7 +14,7 @@ COMMDIR:=communication
 # I know -finline-functions and -finline-functions-called-once are enabled by
 # -O3 but I did this in case gcc behaviour change one day
 CFLAGS:=-c -O3 -finline-functions -finline-functions-called-once -Wall -Wextra -Werror
-LDFLAGS:=-L$(LIBDIR) -lpthread -ldl
+LDFLAGS:=-L$(LIBDIR) -lpthread -ldl -lrt
 
 # Executables
 CC=gcc

communication_techniques/include/batch_queue_common_comm.h

@@ -1,6 +1,9 @@
 #ifndef _BATCH_QUEUE_COMMON_COMM_H_
 #define _BATCH_QUEUE_COMMON_COMM_H_ 1
 
+#include <stdint.h>
+#include <unistd.h>
+
 /* Non standard include */
 #include <commtech.h>
 
@@ -10,27 +13,66 @@
 
 struct channel
 {
-	void * volatile buf[2 * BUF_SIZE / sizeof(void *)] __attribute__ ((aligned (CACHE_LINE_SIZE)));
+	/* buf must be the first field to allow the buf_mask test */
+	void * volatile buf[2][BUF_SIZE / sizeof(void *)] __attribute__ ((aligned (CACHE_LINE_SIZE)));
+	struct channel *mapping1; /* accesses to buf[0] and state */
+	struct channel *mapping2; /* accesses to buf[1] */
+	uintptr_t buf_mask;
 	int unused[20] __attribute__ ((aligned (CACHE_LINE_SIZE)));
 	volatile unsigned int  state:1 __attribute__ ((aligned (CACHE_LINE_SIZE)));
-	unsigned int  sender_idx __attribute__ ((aligned (CACHE_LINE_SIZE)));
+	void * volatile *sender_ptr __attribute__ ((aligned (CACHE_LINE_SIZE)));
-	unsigned int receiver_idx __attribute__ ((aligned (CACHE_LINE_SIZE)));
+	void * volatile *receiver_ptr __attribute__ ((aligned (CACHE_LINE_SIZE)));
 };
 
+#ifndef _BATCH_QUEUE_C_
+#ifndef PAGE_SIZE_HELPER
+#define PAGE_SIZE_HELPER 1
+uintptr_t _bq_page_mask;
+void *create_comm_channel_internal(void);
+static void *create_comm_channel_helper(void) __attribute__ ((unused));
+
+static void *create_comm_channel_helper(void)
+{
+	int ret;
+	struct channel *channel;
+
+	ret = sysconf(_SC_PAGESIZE);
+	if (ret == -1)
+		return NULL;
+	_bq_page_mask = ~(ret - 1);
+	channel = create_comm_channel_internal();
+	channel->buf_mask = sizeof channel->buf[0] - 1;
+	return channel;
+}
+
+#else
+extern unsigned int _bq_page_mask;
+#endif /* PAGE_SIZE_HELPER */
+
+#define create_comm_channel() create_comm_channel_helper()
 
 __BEGIN_DECLS
 
 static inline void send(struct channel *channel, void **addr)
 {
-	channel->buf[channel->sender_idx++] = addr;
+	uintptr_t sender_ptr_high;
-	channel->sender_idx %= 2 * (BUF_SIZE / sizeof(void *));
+
-	if (!(channel->sender_idx % (BUF_SIZE / sizeof(void *))))
+	*channel->sender_ptr++ = addr;
+	if (unlikely(!((uintptr_t) channel->sender_ptr & channel->buf_mask)))
 	{
 		while (channel->state);
 		channel->state = 1;
+		sender_ptr_high =
+			(uintptr_t) channel->sender_ptr & _bq_page_mask;
+		if ((void *) sender_ptr_high == channel->mapping1)
+			channel->sender_ptr = channel->mapping2->buf[1];
+		else
+			channel->sender_ptr = channel->mapping1->buf[0];
 	}
 }
 
 __END_DECLS
 
+#endif /* _BATCH_QUEUE_C_ */
+
 #endif

communication_techniques/src/communication/batch_queue.c

@@ -1,24 +1,93 @@
+#define _BATCH_QUEUE_C_ 1
+
 #include <stdio.h>
 #include <stdlib.h>
-#include <pthread.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <limits.h>
 
 /* Non standard include */
 #include <commtech.h>
 #include <specific_comm.h>
 
+#define BASE_SHM_NAME "/channel"
+#define ROUNDUP(size) ((size + page_size) & ~(page_size - 1))
 
-void *create_comm_channel(void)
+
+static uintptr_t buf_mask;
+static uintptr_t page_mask;
+static int nb_buf_entries;
+static unsigned int page_size;
+
+
+void *create_comm_channel_internal(void)
 {
-	struct channel *channel;
+	int ret, shm_fd;
+	static int chan_idx = 0;
+	char shm_name[NAME_MAX];
+	struct channel *channel1, *channel2;
 
-	if (!posix_memalign((void **) &channel, CACHE_LINE_SIZE, sizeof(struct channel)))
+	channel1 = NULL;
+	channel2 = NULL;
+	ret = sysconf(_SC_PAGESIZE);
+	if (ret == -1)
 	{
-		channel->receiver_idx = 0;
+		perror("BatchQueue init sysconf");
-		channel->state = 0;
+		return NULL;
-		channel->sender_idx = 0;
-		return channel;
 	}
-	return NULL;
+	page_size = ret;
+	page_mask = ~((uintptr_t) (page_size - 1));
+	ret = snprintf(shm_name, NAME_MAX, BASE_SHM_NAME"%d\n", chan_idx);
+	if (ret < 0)
+	{
+		fprintf(stderr, "BatchQueue init snprintf failed\n");
+		return NULL;
+	} else if (ret >= NAME_MAX)
+	{
+		fprintf(stderr, "Too many channels created: impossible to ");
+		fprintf(stderr, "create a channel named "BASE_SHM_NAME);
+		fprintf(stderr, "%d\n", chan_idx);
+		return NULL;
+	}
+	shm_fd = shm_open(shm_name, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
+	if (shm_fd == -1)
+	{
+		perror("BatchQueue init shm_open failed");
+		return NULL;
+	}
+	ret = ftruncate(shm_fd, sizeof(*channel1));
+	if (ret == -1)
+	{
+		perror("BatchQueue init ftruncate failed");
+		goto close_file;
+	}
+	channel1 = mmap(NULL, ROUNDUP(sizeof(*channel1)),
+		PROT_READ | PROT_WRITE, MAP_PRIVATE, shm_fd, 0);
+	channel2 = mmap(NULL, ROUNDUP(sizeof(*channel1)),
+		PROT_READ | PROT_WRITE, MAP_PRIVATE, shm_fd, 0);
+	if ((channel1 == MAP_FAILED) || (channel2 == MAP_FAILED))
+	{
+		perror("Batchqueue init mmap failed");
+		channel1 = NULL;
+		goto close_file;
+	}
+
+	channel1->mapping1 = channel1;
+	channel1->mapping2 = channel2;
+
+	channel1->state = 0;
+
+	channel1->sender_ptr = channel1->buf[0];
+	channel1->receiver_ptr = channel1->buf[0];
+
+	buf_mask = sizeof channel1->buf[0] - 1;
+	nb_buf_entries = sizeof channel1->buf[0] / sizeof channel1->buf[0][0];
+close_file:
+	shm_unlink(shm_name);
+	return channel1;
 }
 
 int end_producer(void *unused __attribute__ ((unused)))
@@ -28,8 +97,17 @@ int end_producer(void *unused __attribute__ ((unused)))
 
 int destroy_comm_channel(void *channel)
 {
-	free(channel);
+	size_t mapping_size;
-	return 0;
+	struct channel *mapping1, *mapping2, *channel_ptr;
+
+	channel_ptr = (struct channel *) channel;
+	mapping1 = channel_ptr->mapping1;
+	mapping2 = channel_ptr->mapping2;
+	mapping_size = ROUNDUP(sizeof(*mapping1));
+	if (munmap(mapping1, mapping_size) || munmap(mapping2, mapping_size))
+		return -1;
+	else
+		return 0;
 }
 
 /*
@@ -44,12 +122,20 @@ void *recv_one_data(struct channel *channel)
 {
 	void *result;
 
-	if (unlikely(!(channel->receiver_idx % (BUF_SIZE / sizeof(void *)))))
+	if (unlikely(!((uintptr_t) channel->receiver_ptr & buf_mask)))
 		while (!channel->state);
-	result = channel->buf[channel->receiver_idx++];
+	result = *channel->receiver_ptr++;
-	channel->receiver_idx %= (2 * BUF_SIZE) / sizeof(void *);
+	if (unlikely(!((uintptr_t) channel->receiver_ptr & buf_mask)))
-	if (unlikely(!(channel->receiver_idx % (BUF_SIZE / sizeof(void *)))))
+	{
+		uintptr_t rcvr_ptr_high;
+
+		rcvr_ptr_high = (uintptr_t) channel->receiver_ptr & page_mask;
 		channel->state = 0;
+		if ((void *) rcvr_ptr_high == channel->mapping1)
+			channel->receiver_ptr = channel->mapping2->buf[1];
+		else
+			channel->receiver_ptr = channel->mapping1->buf[0];
+	}
 	return result;
 }
 
@@ -69,21 +155,20 @@ ssize_t recv_some_data(struct channel *channel, void **buf, size_t count)
 	nb_read = 0;
 	while (channel->state && nb_read < count)
 	{
-		int i, n;
+		void * volatile *chanbuf_ptr;
-		/*
+		uintptr_t rcvr_ptr_high;
-		 * cur->receiver_idx point to the last buffer we have read.
+
-		 * We go to the next cache line "+ (BUF_SIZE / sizeof(void *))"
+		chanbuf_ptr = channel->receiver_ptr;
-		 * (because the line is full of void * and then if we are after
+		channel->receiver_ptr += nb_buf_entries;
-		 * the second cache line we correct the pointer to point to the
+		rcvr_ptr_high = (uintptr_t) channel->receiver_ptr & page_mask;
-		 * first one (this is done by the modulo).
+		for(; chanbuf_ptr != channel->receiver_ptr; chanbuf_ptr++)
-		 */
+			*buf++ = *chanbuf_ptr;
-		i = channel->receiver_idx;
+		nb_read += nb_buf_entries;
-		n = channel->receiver_idx + (BUF_SIZE / sizeof(void *));
-		channel->receiver_idx = n % ((2 * BUF_SIZE) / sizeof(void *));
-		for(; i < n; i++)
-			*buf++ = channel->buf[i];
-		nb_read += BUF_SIZE / sizeof(void *);
 		channel->state = 0;
+		if ((void *) rcvr_ptr_high == channel->mapping1)
+			channel->receiver_ptr = channel->mapping2->buf[1];
+		else
+			channel->receiver_ptr = channel->mapping1->buf[0];
 	}
 	return nb_read;
 }

communication_techniques/src/main.c

@@ -465,7 +465,8 @@ static int consumer_data(node_param_t *node_param)
 		}
 	}
 	cons_check_value = init_calc_arg;
-	for(i = 0; i < nb_bufs_sent; i++) {
+	for(i = 0; i < nb_bufs_sent; i++)
+	{
 		for(j = 0; j < WORDS_PER_LINE; j++)
 		{
 			void *data;