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NTB: Default to CPU memcpy for performance

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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>
Signed-off-by: Jon Mason <jdmason@kudzu.us>
This commit is contained in:
Dave Jiang 2015-05-19 16:52:04 -04:00 committed by Jon Mason
parent 06917f7535
commit a41ef053f7
1 changed files with 13 additions and 4 deletions
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17
drivers/ntb/ntb_transport.c
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@ -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 {
@ -1589,10 +1593,15 @@ 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);