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tracing/events: Add bounce tracing to swiotbl

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Ftrace is currently not able to detect when SWIOTLB has to do double buffering.
Under Xen you can only see it indirectly in function_graph, when
xen_swiotlb_map_page() doesn't stop after range_straddles_page_boundary(), but
calls spinlock functions, memcpy() and xen_phys_to_bus() as well. This patch
introduces the swiotlb:swiotlb_bounced event, which also prints out the
following informations to help you find out why bouncing happened:

dev_name: 0000:08:00.0 dma_mask=ffffffffffffffff dev_addr=9149f000 size=32768
swiotlb_force=0

If you use Xen, and (dev_addr + size + 1) > dma_mask, the buffer is out of the
device's DMA range. If swiotlb_force == 1, you should really change the kernel
parameters. Otherwise, the buffer is not contiguous in mfn space.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
[v1: Don't print 'swiotlb_force=X', just print swiotlb_force if it is enabled]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Zoltan Kiss 2013-09-04 21:11:05 +01:00 • committed by Konrad Rzeszutek Wilk
parent 04b772d2b8
commit 2b2b614dd2
3 changed files with 55 additions and 0 deletions
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4
lib/swiotlb.c
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@ -38,6 +38,8 @@
#include <linux/bootmem.h>
#include <linux/iommu-helper.h>
#include <trace/events/swiotlb.h>
#define OFFSET(val,align) ((unsigned long) \
( (val) & ( (align) - 1)))
@ -726,6 +728,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
if (dma_capable(dev, dev_addr, size) && !swiotlb_force)
return dev_addr;
trace_swiotlb_bounced(dev, dev_addr, size, swiotlb_force);
/* Oh well, have to allocate and map a bounce buffer. */
map = map_single(dev, phys, size, dir);
if (map == SWIOTLB_MAP_ERROR) {