linux-kernel - Re: [PATCH v4] bus: mhi: host: Add tracing support

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Date:   Sat, 11 Nov 2023 14:37:10 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Krishna chaitanya chundru <quic_krichai@...cinc.com>
Cc:     Manivannan Sadhasivam <mani@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        <linux-kernel@...r.kernel.org>, <mhi@...ts.linux.dev>,
        <linux-arm-msm@...r.kernel.org>,
        <linux-trace-kernel@...r.kernel.org>, <quic_vbadigan@...cinc.com>,
        <quic_ramkri@...cinc.com>, <quic_nitegupt@...cinc.com>,
        <quic_skananth@...cinc.com>, <quic_parass@...cinc.com>
Subject: Re: [PATCH v4] bus: mhi: host: Add tracing support

On Sat, 11 Nov 2023 11:25:22 +0530
Krishna chaitanya chundru <quic_krichai@...cinc.com> wrote:
> diff --git a/drivers/bus/mhi/host/trace.h b/drivers/bus/mhi/host/trace.h
> new file mode 100644
> index 000000000000..0e99318f5d08
> --- /dev/null
> +++ b/drivers/bus/mhi/host/trace.h
> +
> +TRACE_EVENT(mhi_update_channel_state_start,
> +
> +	TP_PROTO(const char *name, int ch_num, int state),
> +
> +	TP_ARGS(name, ch_num, state),
> +
> +	TP_STRUCT__entry(
> +		__string(name, name)
> +		__field(int, ch_num)
> +		__field(int, state)
> +	),
> +
> +	TP_fast_assign(
> +		__assign_str(name, name);
> +		__entry->ch_num = ch_num;
> +		__entry->state = state;
> +	),
> +
> +	TP_printk("%s: ch%d: Updating state to: %s\n",
> +		  __get_str(name), __entry->ch_num,
> +		  TO_CH_STATE_TYPE_STR(__entry->state))
> +);
> +
> +TRACE_EVENT(mhi_update_channel_state_end,
> +
> +	TP_PROTO(const char *name, int ch_num, int state),
> +
> +	TP_ARGS(name, ch_num, state),
> +
> +	TP_STRUCT__entry(
> +		__string(name, name)
> +		__field(int, ch_num)
> +		__field(int, state)
> +	),
> +
> +	TP_fast_assign(
> +		__assign_str(name, name);
> +		__entry->ch_num = ch_num;
> +		__entry->state = state;
> +	),
> +
> +	TP_printk("%s: ch%d: Updated state to: %s\n",
> +		  __get_str(name), __entry->ch_num,
> +		  TO_CH_STATE_TYPE_STR(__entry->state))
> +);
> +

The above three events have the same format. You can save kilobytes of
memory by converting them into a DECLARE_EVENT_CLASS() and use
DEFINE_EVENT() for each event.

A TRACE_EVENT() macro is really just a wrapper around
DECLARE_EVENT_CLASS() and DEFINE_EVENT(). The DECLARE_EVENT_CLASS()
does the bulk of the work and adds the most memory footprint. By
breaking it apart for several events, it does save memory.

Whenever you can use a single DECLARE_EVENT_CLASS() for multiple
events, I strongly suggest doing so.

Thanks,

-- Steve


> +#endif
> +#undef TRACE_INCLUDE_PATH
> +#define TRACE_INCLUDE_PATH .
> +#undef TRACE_INCLUDE_FILE
> +#define TRACE_INCLUDE_FILE trace
> +
> +#include <trace/define_trace.h>
> 
> ---
> base-commit: 3006adf3be79cde4d14b1800b963b82b6e5572e0
> change-id: 20231005-ftrace_support-6869d4156139
> 
> Best regards,