Re: [PATCH 1/2] Add TRACE_EVENTs in pwc_isoc_handler()

Steven Rostedt
2018-06-18T18:58:57Z

On Sun, 17 Jun 2018 17:36:24 +0300
"Matwey V. Kornilov" <matwey@sai.msu.ru> wrote:

I would prefer a change log here that would explain why these
tracepoints are being added.

> Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
> ---
> drivers/media/usb/pwc/pwc-if.c | 7 +++++++
> include/trace/events/pwc.h | 45 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 52 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..5775d1f60668 100644
> --- a/drivers/media/usb/pwc/pwc-if.c
> +++ b/drivers/media/usb/pwc/pwc-if.c
> @@ -57,6 +57,9 @@
> - Pham Thanh Nam: webcam snapshot button as an event input device
> */
>
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/pwc.h>
> +
> #include <linux/errno.h>
> #include <linux/init.h>
> #include <linux/mm.h>
> @@ -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);
> +
> if (urb->status == -ENOENT || urb->status == -ECONNRESET ||
> urb->status == -ESHUTDOWN) {
> PWC_DEBUG_OPEN("URB (%p) unlinked %ssynchronously.\n",

Looks like if this is hit, we will return from the function without
calling trace_pwc_handler_exit().

> @@ -347,6 +352,8 @@ static void pwc_isoc_handler(struct urb *urb)
> pdev->vlast_packet_size = flen;
> }
>
> + trace_pwc_handler_exit(urb);
> +
> handler_end:

Why not add the tracepoint after handler_end. In fact, why not add some
exit status to the trace event? I would think that would be useful as
well.

> i = usb_submit_urb(urb, GFP_ATOMIC);
> if (i != 0)
> diff --git a/include/trace/events/pwc.h b/include/trace/events/pwc.h
> new file mode 100644
> index 000000000000..b13d2118bb7a
> --- /dev/null
> +++ b/include/trace/events/pwc.h
> @@ -0,0 +1,45 @@
> +/* 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),
> + TP_ARGS(urb),
> + TP_STRUCT__entry(
> + __field(struct urb*, urb)
> + __field(int, urb__status)
> + __field(u32, urb__actual_length)
> + ),
> + TP_fast_assign(
> + __entry->urb = urb;
> + __entry->urb__status = urb->status;
> + __entry->urb__actual_length = urb->actual_length;

Is there any other data that may be interesting to record here?

-- Steve

> + ),
> + TP_printk("urb=%p (status=%d actual_length=%u)",
> + __entry->urb,
> + __entry->urb__status,
> + __entry->urb__actual_length)
> +);
> +
> +TRACE_EVENT(pwc_handler_exit,
> + TP_PROTO(struct urb *urb),
> + TP_ARGS(urb),
> + TP_STRUCT__entry(
> + __field(struct urb*, urb)
> + ),
> + TP_fast_assign(
> + __entry->urb = urb;
> + ),
> + TP_printk("urb=%p", __entry->urb)
> +);
> +
> +#endif /* _TRACE_PWC_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>