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Re: [Xen-devel] [PATCH] tracing/events: Add bounce tracing to swiotbl-xen

On 23/08/13 13:55, Konrad Rzeszutek Wilk wrote:
On Thu, Aug 22, 2013 at 10:47:28PM +0100, Zoltan Kiss wrote:
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-xen: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

If (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.

Could this be in the lib/swiotlb.c instead?

You mean instead of drivers/xen/swiotlb-xen.c ? This is a Xen SWIOTLB specific thing, it will hit exactly at the point when double buffering becomes sure - under Xen. But I can rename the tracer and call trace_bounced in swiotlb_map_page as well, so it can be used for normal SWIOTLB bounce tracing as well. Is it OK for you?



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