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Subject[PATCH v2] dma-mapping: benchmark: pretend DMA is transmitting
Date
In a real dma mapping user case, after dma_map is done, data will be
transmit. Thus, in multi-threaded user scenario, IOMMU contention
should not be that severe. For example, if users enable multiple
threads to send network packets through 1G/10G/100Gbps NIC, usually
the steps will be: map -> transmission -> unmap. Transmission delay
reduces the contention of IOMMU.

Here a delay is added to simulate the transmission between map and unmap
so that the tested result could be more accurate for TX and simple RX.
A typical TX transmission for NIC would be like: map -> TX -> unmap
since the socket buffers come from OS. Simple RX model eg. disk driver,
is also map -> RX -> unmap, but real RX model in a NIC could be more
complicated considering packets can come spontaneously and many drivers
are using pre-mapped buffers pool. This is in the TBD list.

Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
---
-v2: cleanup according to Robin's feedback. thanks, Robin.

kernel/dma/map_benchmark.c | 10 ++++++++++
.../testing/selftests/dma/dma_map_benchmark.c | 19 +++++++++++++++++--
2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/kernel/dma/map_benchmark.c b/kernel/dma/map_benchmark.c
index 1b1b8ff875cb..06636406a245 100644
--- a/kernel/dma/map_benchmark.c
+++ b/kernel/dma/map_benchmark.c
@@ -21,6 +21,7 @@
#define DMA_MAP_BENCHMARK _IOWR('d', 1, struct map_benchmark)
#define DMA_MAP_MAX_THREADS 1024
#define DMA_MAP_MAX_SECONDS 300
+#define DMA_MAP_MAX_TRANS_DELAY (10 * NSEC_PER_MSEC) /* 10ms */

#define DMA_MAP_BIDIRECTIONAL 0
#define DMA_MAP_TO_DEVICE 1
@@ -36,6 +37,7 @@ struct map_benchmark {
__s32 node; /* which numa node this benchmark will run on */
__u32 dma_bits; /* DMA addressing capability */
__u32 dma_dir; /* DMA data direction */
+ __u32 dma_trans_ns; /* time for DMA transmission in ns */
__u64 expansion[10]; /* For future use */
};

@@ -87,6 +89,9 @@ static int map_benchmark_thread(void *data)
map_etime = ktime_get();
map_delta = ktime_sub(map_etime, map_stime);

+ /* Pretend DMA is transmitting */
+ ndelay(map->bparam.dma_trans_ns);
+
unmap_stime = ktime_get();
dma_unmap_single(map->dev, dma_addr, PAGE_SIZE, map->dir);
unmap_etime = ktime_get();
@@ -218,6 +223,11 @@ static long map_benchmark_ioctl(struct file *file, unsigned int cmd,
return -EINVAL;
}

+ if (map->bparam.dma_trans_ns > DMA_MAP_MAX_TRANS_DELAY) {
+ pr_err("invalid transmission delay\n");
+ return -EINVAL;
+ }
+
if (map->bparam.node != NUMA_NO_NODE &&
!node_possible(map->bparam.node)) {
pr_err("invalid numa node\n");
diff --git a/tools/testing/selftests/dma/dma_map_benchmark.c b/tools/testing/selftests/dma/dma_map_benchmark.c
index 7065163a8388..a370290d9503 100644
--- a/tools/testing/selftests/dma/dma_map_benchmark.c
+++ b/tools/testing/selftests/dma/dma_map_benchmark.c
@@ -11,9 +11,12 @@
#include <sys/mman.h>
#include <linux/types.h>

+#define NSEC_PER_MSEC 1000000L
+
#define DMA_MAP_BENCHMARK _IOWR('d', 1, struct map_benchmark)
#define DMA_MAP_MAX_THREADS 1024
#define DMA_MAP_MAX_SECONDS 300
+#define DMA_MAP_MAX_TRANS_DELAY (10 * NSEC_PER_MSEC) /* 10ms */

#define DMA_MAP_BIDIRECTIONAL 0
#define DMA_MAP_TO_DEVICE 1
@@ -35,6 +38,7 @@ struct map_benchmark {
__s32 node; /* which numa node this benchmark will run on */
__u32 dma_bits; /* DMA addressing capability */
__u32 dma_dir; /* DMA data direction */
+ __u32 dma_trans_ns; /* delay for DMA transmission in ns */
__u64 expansion[10]; /* For future use */
};

@@ -45,12 +49,12 @@ int main(int argc, char **argv)
/* default single thread, run 20 seconds on NUMA_NO_NODE */
int threads = 1, seconds = 20, node = -1;
/* default dma mask 32bit, bidirectional DMA */
- int bits = 32, dir = DMA_MAP_BIDIRECTIONAL;
+ int bits = 32, xdelay = 0, dir = DMA_MAP_BIDIRECTIONAL;

int cmd = DMA_MAP_BENCHMARK;
char *p;

- while ((opt = getopt(argc, argv, "t:s:n:b:d:")) != -1) {
+ while ((opt = getopt(argc, argv, "t:s:n:b:d:x:")) != -1) {
switch (opt) {
case 't':
threads = atoi(optarg);
@@ -67,6 +71,9 @@ int main(int argc, char **argv)
case 'd':
dir = atoi(optarg);
break;
+ case 'x':
+ xdelay = atoi(optarg);
+ break;
default:
return -1;
}
@@ -84,6 +91,12 @@ int main(int argc, char **argv)
exit(1);
}

+ if (xdelay < 0 || xdelay > DMA_MAP_MAX_TRANS_DELAY) {
+ fprintf(stderr, "invalid transmit delay, must be in 0-%ld\n",
+ DMA_MAP_MAX_TRANS_DELAY);
+ exit(1);
+ }
+
/* suppose the mininum DMA zone is 1MB in the world */
if (bits < 20 || bits > 64) {
fprintf(stderr, "invalid dma mask bit, must be in 20-64\n");
@@ -107,6 +120,8 @@ int main(int argc, char **argv)
map.node = node;
map.dma_bits = bits;
map.dma_dir = dir;
+ map.dma_trans_ns = xdelay;
+
if (ioctl(fd, cmd, &map)) {
perror("ioctl");
exit(1);
--
2.25.1
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