linux-kernel - Re: [PATCH] tracing/events: Add bounce tracing to swiotbl-xen

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Message-ID: <20130823125533.GC14306@konrad-lan.dumpdata.com>
Date:	Fri, 23 Aug 2013 08:55:33 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xensource.com,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] tracing/events: Add bounce tracing to swiotbl-xen

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@...rix.com>
> ---
>  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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