[PATCH v2 15/17] NTB: Default to CPU memcpy for performance

Allen Hubbe
2015-05-21T13:31:28Z

From: Dave Jiang <dave.jiang@intel.com>

Disable DMA usage by default, since the CPU provides much better
performance with write combining. Provide a module parameter to enable
DMA usage when offloading the memcpy is preferred.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Allen Hubbe <Allen.Hubbe@emc.com>
---
drivers/ntb/ntb_transport.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index 95252ea..9c266e1 100644
--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -88,6 +88,10 @@ static unsigned int copy_bytes = 1024;
module_param(copy_bytes, uint, 0644);
MODULE_PARM_DESC(copy_bytes, "Threshold under which NTB will use the CPU to copy instead of DMA");

+static bool use_dma;
+module_param(use_dma, bool, 0644);
+MODULE_PARM_DESC(use_dma, "Use DMA engine to perform large data copy");
+
static struct dentry *nt_debugfs_dir;

struct ntb_queue_entry {
@@ -1571,10 +1575,15 @@ ntb_transport_create_queue(void *data, struct device *client_dev,
dma_cap_zero(dma_mask);
dma_cap_set(DMA_MEMCPY, dma_mask);

- qp->dma_chan = dma_request_channel(dma_mask, ntb_dma_filter_fn,
- (void *)(unsigned long)node);
- if (!qp->dma_chan)
- dev_info(&pdev->dev, "Unable to allocate DMA channel, using CPU instead\n");
+ if (use_dma) {
+ qp->dma_chan = dma_request_channel(dma_mask, ntb_dma_filter_fn,
+ (void *)(unsigned long)node);
+ if (!qp->dma_chan)
+ dev_info(&pdev->dev, "Unable to allocate DMA channel\n");
+ } else {
+ qp->dma_chan = NULL;
+ }
+ dev_dbg(&pdev->dev, "Using %s memcpy\n", qp->dma_chan ? "DMA" : "CPU");

for (i = 0; i < NTB_QP_DEF_NUM_ENTRIES; i++) {
entry = kzalloc_node(sizeof(*entry), GFP_ATOMIC, node);
--
2.4.0.rc0.43.gcf8a8c6