linux-kernel - Re: [PATCH v3 1/2] media: usb: pwc: Introduce TRACE_EVENTs for pwc_isoc

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Date:   Thu, 9 Aug 2018 09:49:30 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Matwey V. Kornilov" <matwey@....msu.ru>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        tfiga@...omium.org, laurent.pinchart@...asonboard.com,
        stern@...land.harvard.edu, ezequiel@...labora.com,
        hdegoede@...hat.com, hverkuil@...all.nl, mchehab@...nel.org,
        mingo@...hat.com, isely@...ox.com, bhumirks@...il.com,
        colin.king@...onical.com, kieran.bingham@...asonboard.com,
        keiichiw@...omium.org
Subject: Re: [PATCH v3 1/2] media: usb: pwc: Introduce TRACE_EVENTs for
 pwc_isoc_handler()

On Thu,  9 Aug 2018 12:33:06 +0300
"Matwey V. Kornilov" <matwey@....msu.ru> wrote:

> There were reports that PWC-based webcams don't work at some
> embedded ARM platforms. [1] Isochronous transfer handler seems to
> work too long leading to the issues in MUSB USB host subsystem.
> Also note, that urb->giveback() handlers are still called with
> disabled interrupts. In order to be able to measure performance of
> PWC driver, traces are introduced in URB handler section.
> 
> [1] https://www.spinics.net/lists/linux-usb/msg165735.html
> 
> Signed-off-by: Matwey V. Kornilov <matwey@....msu.ru>
> ---
>  drivers/media/usb/pwc/pwc-if.c |  7 +++++
>  include/trace/events/pwc.h     | 64 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 71 insertions(+)
>  create mode 100644 include/trace/events/pwc.h
> 
> diff --git a/drivers/media/usb/pwc/pwc-if.c b/drivers/media/usb/pwc/pwc-if.c
> index 54b036d39c5b..72d2897a4b9f 100644
> --- a/drivers/media/usb/pwc/pwc-if.c
> +++ b/drivers/media/usb/pwc/pwc-if.c
> @@ -76,6 +76,9 @@
>  #include "pwc-dec23.h"
>  #include "pwc-dec1.h"
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/pwc.h>
> +
>  /* Function prototypes and driver templates */
>  
>  /* hotplug device table support */
> @@ -260,6 +263,8 @@ static void pwc_isoc_handler(struct urb *urb)
>  	int i, fst, flen;
>  	unsigned char *iso_buf = NULL;
>  
> +	trace_pwc_handler_enter(urb, pdev);
> +
>  	if (urb->status == -ENOENT || urb->status == -ECONNRESET ||
>  	    urb->status == -ESHUTDOWN) {
>  		PWC_DEBUG_OPEN("URB (%p) unlinked %ssynchronously.\n",
> @@ -348,6 +353,8 @@ static void pwc_isoc_handler(struct urb *urb)
>  	}
>  
>  handler_end:
> +	trace_pwc_handler_exit(urb, pdev);
> +
>  	i = usb_submit_urb(urb, GFP_ATOMIC);
>  	if (i != 0)
>  		PWC_ERROR("Error (%d) re-submitting urb in pwc_isoc_handler.\n", i);
> diff --git a/include/trace/events/pwc.h b/include/trace/events/pwc.h
> new file mode 100644
> index 000000000000..71ba98770537
> --- /dev/null
> +++ b/include/trace/events/pwc.h
> @@ -0,0 +1,64 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#if !defined(_TRACE_PWC_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_PWC_H
> +
> +#include <linux/usb.h>
> +#include <linux/tracepoint.h>
> +
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM pwc
> +
> +TRACE_EVENT(pwc_handler_enter,
> +	TP_PROTO(struct urb *urb, struct pwc_device *pdev),
> +	TP_ARGS(urb, pdev),
> +	TP_STRUCT__entry(
> +		__field(struct urb*, urb)
> +		__field(int, urb__status)
> +		__field(u32, urb__actual_length)
> +		__field(const char*, name)

name needs to be a __string. Never save pointers that you will
dereference in the print_fmt, as you never know if those pointers will
exist later. Not to mention, userspace tools like trace-cmd and perf
have no idea how to display them.

You want:

		__string( name, pdev->v4l2_dev.name ),


> +		__field(struct pwc_frame_buf*, fbuf)
> +		__field(int, fbuf__filled)
> +	),
> +	TP_fast_assign(
> +		__entry->urb = urb;
> +		__entry->urb__status = urb->status;
> +		__entry->urb__actual_length = urb->actual_length;
> +		__entry->name = pdev->v4l2_dev.name;

And here you assign it with:

		__assign_str(name, pdev->v4l2_dev.name);

> +		__entry->fbuf = pdev->fill_buf;
> +		__entry->fbuf__filled = (pdev->fill_buf ? pdev->fill_buf->filled : 0);
> +	),
> +	TP_printk("dev=%s (fbuf=%p filled=%d) urb=%p (status=%d actual_length=%u)",
> +		__entry->name,

And display it with:

		__get_str(name),

> +		__entry->fbuf,
> +		__entry->fbuf__filled,
> +		__entry->urb,
> +		__entry->urb__status,
> +		__entry->urb__actual_length)
> +);
> +
> +TRACE_EVENT(pwc_handler_exit,
> +	TP_PROTO(struct urb *urb, struct pwc_device* pdev),
> +	TP_ARGS(urb, pdev),
> +	TP_STRUCT__entry(
> +		__field(struct urb*, urb)
> +		__field(const char*, name)
> +		__field(struct pwc_frame_buf*, fbuf)
> +		__field(int, fbuf__filled)
> +	),
> +	TP_fast_assign(
> +		__entry->urb = urb;
> +		__entry->name = pdev->v4l2_dev.name;
> +		__entry->fbuf = pdev->fill_buf;
> +		__entry->fbuf__filled = pdev->fill_buf->filled;
> +	),
> +	TP_printk(" dev=%s (fbuf=%p filled=%d) urb=%p",
> +		__entry->name,

Same thing here.

-- Steve

> +		__entry->fbuf,
> +		__entry->fbuf__filled,
> +		__entry->urb)
> +);
> +
> +#endif /* _TRACE_PWC_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>