Optimise allocation of USB DMA structures. By default don't double map

allocations if only one element should be allocated per page
cache. Make one allocation per element compile time configurable. Fix
a comment while at it.

Suggested by:	ian @
MFC after:	1 week

1 files changed, 27 insertions, 4 deletions

diff --git a/sys/dev/usb/usb_transfer.c b/sys/dev/usb/usb_transfer.c
index 0f02fc8..5650790 100644
--- a/sys/dev/usb/usb_transfer.c
+++ b/sys/dev/usb/usb_transfer.c
@@ -237,7 +237,11 @@ usbd_transfer_setup_sub_malloc(struct usb_setup_params *parm,
 		n_obj = 1;
 	} else {
 		/* compute number of objects per page */
+#ifdef USB_DMA_SINGLE_ALLOC
+		n_obj = 1;
+#else
 		n_obj = (USB_PAGE_SIZE / size);
+#endif
 		/*
 		 * Compute number of DMA chunks, rounded up
 		 * to nearest one:
@@ -273,15 +277,33 @@ usbd_transfer_setup_sub_malloc(struct usb_setup_params *parm,
 		    &parm->curr_xfer->xroot->dma_parent_tag;
 	}
 
-	if (ppc) {
-		*ppc = parm->xfer_page_cache_ptr;
+	if (ppc != NULL) {
+		if (n_obj != 1)
+			*ppc = parm->xfer_page_cache_ptr;
+		else
+			*ppc = parm->dma_page_cache_ptr;
 	}
 	r = count;			/* set remainder count */
 	z = n_obj * size;		/* set allocation size */
 	pc = parm->xfer_page_cache_ptr;
 	pg = parm->dma_page_ptr;
 
-	for (x = 0; x != n_dma_pc; x++) {
+	if (n_obj == 1) {
+	    /*
+	     * Avoid mapping memory twice if only a single object
+	     * should be allocated per page cache:
+	     */
+	    for (x = 0; x != n_dma_pc; x++) {
+		if (usb_pc_alloc_mem(parm->dma_page_cache_ptr,
+		    pg, z, align)) {
+			return (1);	/* failure */
+		}
+		/* Make room for one DMA page cache and "n_dma_pg" pages */
+		parm->dma_page_cache_ptr++;
+		pg += n_dma_pg;
+	    }
+	} else {
+	    for (x = 0; x != n_dma_pc; x++) {
 
 		if (r < n_obj) {
 			/* compute last remainder */
@@ -294,7 +316,7 @@ usbd_transfer_setup_sub_malloc(struct usb_setup_params *parm,
 		}
 		/* Set beginning of current buffer */
 		buf = parm->dma_page_cache_ptr->buffer;
-		/* Make room for one DMA page cache and one page */
+		/* Make room for one DMA page cache and "n_dma_pg" pages */
 		parm->dma_page_cache_ptr++;
 		pg += n_dma_pg;
 
@@ -314,6 +336,7 @@ usbd_transfer_setup_sub_malloc(struct usb_setup_params *parm,
 			}
 			mtx_unlock(pc->tag_parent->mtx);
 		}
+	    }
 	}
 
 	parm->xfer_page_cache_ptr = pc;