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

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

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.

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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