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

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Date:	Mon, 2 Sep 2013 18:54:30 +0100
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.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 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
>> 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?

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?

Regards,

Zoli
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