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
> swiotlb_force=0
>
> 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?
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
> ---
> drivers/xen/swiotlb-xen.c | 7 ++++++
> include/trace/events/swiotlb-xen.h | 46 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 53 insertions(+)
> create mode 100644 include/trace/events/swiotlb-xen.h
>
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index aadffcf..f08440d 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -42,6 +42,10 @@
> #include <xen/page.h>
> #include <xen/xen-ops.h>
> #include <xen/hvc-console.h>
> +
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/swiotlb-xen.h>
> +
> /*
> * Used to do a quick range check in swiotlb_tbl_unmap_single and
> * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
> @@ -358,6 +362,9 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
> /*
> * Oh well, have to allocate and map a bounce buffer.
> */
> +
> + trace_bounced(dev, dev_addr, size, swiotlb_force);
> +
> map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir);
> if (map == SWIOTLB_MAP_ERROR)
> return DMA_ERROR_CODE;
> diff --git a/include/trace/events/swiotlb-xen.h b/include/trace/events/swiotlb-xen.h
> new file mode 100644
> index 0000000..cbe2dca
> --- /dev/null
> +++ b/include/trace/events/swiotlb-xen.h
> @@ -0,0 +1,46 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM swiotlb-xen
> +
> +#if !defined(_TRACE_SWIOTLBXEN_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_SWIOTLBXEN_H
> +
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(bounced,
> +
> + TP_PROTO(struct device *dev,
> + dma_addr_t dev_addr,
> + size_t size,
> + int swiotlb_force),
> +
> + TP_ARGS(dev, dev_addr, size, swiotlb_force),
> +
> + TP_STRUCT__entry(
> + __string( dev_name, dev_name(dev) )
> + __field( u64, dma_mask )
> + __field( dma_addr_t, dev_addr )
> + __field( size_t, size )
> + __field( int, swiotlb_force )
> + ),
> +
> + TP_fast_assign(
> + __assign_str(dev_name, dev_name(dev));
> + __entry->dma_mask = (dev->dma_mask ? *dev->dma_mask : 0);
> + __entry->dev_addr = dev_addr;
> + __entry->size = size;
> + __entry->swiotlb_force = swiotlb_force;
> + ),
> +
> + TP_printk("dev_name: %s dma_mask=%llx dev_addr=%llx "
> + "size=%zu swiotlb_force=%x",
> + __get_str(dev_name),
> + __entry->dma_mask,
> + (unsigned long long)__entry->dev_addr,
> + __entry->size,
> + __entry->swiotlb_force )
> +);
> +
> +#endif /* _TRACE_IRQ_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> --
> 1.7.9.5
>
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