linux-kernel - Re: [PATCH v13 5/8] perf record: Read from overwritable ring buffer

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Date:	Wed, 6 Jul 2016 13:38:57 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	acme@...nel.org, linux-kernel@...r.kernel.org, pi3orama@....com,
	lizefan@...wei.com, He Kuang <hekuang@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH v13 5/8] perf record: Read from overwritable ring buffer

On Mon, Jul 04, 2016 at 06:20:06AM +0000, Wang Nan wrote:

SNIP

> +static void
> +record__toggle_overwrite_evsels(struct record *rec,
> +				enum overwrite_evt_state state)
> +{
> +	struct perf_evlist *evlist = rec->overwrite_evlist;
> +	enum overwrite_evt_state old_state = rec->overwrite_evt_state;
> +	enum action {
> +		NONE,
> +		PAUSE,
> +		RESUME,
> +	} action = NONE;
> +
> +	switch (old_state) {
> +	case OVERWRITE_EVT_RUNNING: {
> +		switch (state) {
> +		case OVERWRITE_EVT_DATA_PENDING:
> +			action = PAUSE;
> +			break;
> +		case OVERWRITE_EVT_RUNNING:
> +		case OVERWRITE_EVT_EMPTY:
> +		default:
> +			goto state_err;
> +		}
> +		break;
> +	}
> +	case OVERWRITE_EVT_DATA_PENDING: {
> +		switch (state) {
> +		case OVERWRITE_EVT_EMPTY:
> +			break;
> +		case OVERWRITE_EVT_RUNNING:
> +		case OVERWRITE_EVT_DATA_PENDING:
> +		default:
> +			goto state_err;
> +		}
> +		break;
> +	}
> +	case OVERWRITE_EVT_EMPTY: {
> +		switch (state) {
> +		case OVERWRITE_EVT_RUNNING:
> +			action = RESUME;
> +			break;
> +		case OVERWRITE_EVT_EMPTY:
> +		case OVERWRITE_EVT_DATA_PENDING:
> +		default:
> +			goto state_err;
> +		}
> +		break;
> +	}
> +	default:
> +		WARN_ONCE(1, "Shouldn't get there\n");
> +	}
> +
> +	rec->overwrite_evt_state = state;
> +
> +	if (!evlist)
> +		return;

I'd expect this check at the begining

jirka