Re: [PATCH 09/10] time_stats: report information in json format

[Darrick J. Wong]

On Fri, Feb 23, 2024 at 05:12:26PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@xxxxxxxxxx>
> 
> Export json versions of time statistics information.  Given the tabular
> nature of the numbers exposed, this will make it a lot easier for higher
> (than C) level languages (e.g. python) to import information without
> needing to write yet another clumsy string parser.
> 
> Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> ---
>  include/linux/time_stats.h |    2 +
>  lib/time_stats.c           |   87 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 89 insertions(+)
> 
> 
> diff --git a/include/linux/time_stats.h b/include/linux/time_stats.h
> index b3c810fff963a..4e1f5485ed039 100644
> --- a/include/linux/time_stats.h
> +++ b/include/linux/time_stats.h
> @@ -156,6 +156,8 @@ static inline bool track_event_change(struct time_stats *stats, bool v)
>  struct seq_buf;
>  void time_stats_to_seq_buf(struct seq_buf *, struct time_stats *,
>  		const char *epoch_name, unsigned int flags);
> +void time_stats_to_json(struct seq_buf *, struct time_stats *,
> +		const char *epoch_name, unsigned int flags);
>  
>  void time_stats_exit(struct time_stats *);
>  void time_stats_init(struct time_stats *);
> diff --git a/lib/time_stats.c b/lib/time_stats.c
> index 0fb3d854e503b..c0f209dd9f6dd 100644
> --- a/lib/time_stats.c
> +++ b/lib/time_stats.c
> @@ -266,6 +266,93 @@ void time_stats_to_seq_buf(struct seq_buf *out, struct time_stats *stats,
>  }
>  EXPORT_SYMBOL_GPL(time_stats_to_seq_buf);
>  
> +void time_stats_to_json(struct seq_buf *out, struct time_stats *stats,
> +		const char *epoch_name, unsigned int flags)
> +{
> +	struct quantiles *quantiles = time_stats_to_quantiles(stats);
> +	s64 f_mean = 0, d_mean = 0;
> +	u64 f_stddev = 0, d_stddev = 0;
> +
> +	if (stats->buffer) {
> +		int cpu;
> +
> +		spin_lock_irq(&stats->lock);
> +		for_each_possible_cpu(cpu)
> +			__time_stats_clear_buffer(stats, per_cpu_ptr(stats->buffer, cpu));
> +		spin_unlock_irq(&stats->lock);
> +	}
> +
> +	if (stats->freq_stats.n) {
> +		/* avoid divide by zero */
> +		f_mean = mean_and_variance_get_mean(stats->freq_stats);
> +		f_stddev = mean_and_variance_get_stddev(stats->freq_stats);
> +		d_mean = mean_and_variance_get_mean(stats->duration_stats);
> +		d_stddev = mean_and_variance_get_stddev(stats->duration_stats);
> +	} else if (flags & TIME_STATS_PRINT_NO_ZEROES) {
> +		/* unless we didn't want zeroes anyway */
> +		return;
> +	}
> +
> +	seq_buf_printf(out, "{\n");
> +	seq_buf_printf(out, "  \"epoch\":       \"%s\",\n", epoch_name);
> +	seq_buf_printf(out, "  \"count\":       %llu,\n", stats->duration_stats.n);
> +
> +	seq_buf_printf(out, "  \"duration_ns\": {\n");
> +	seq_buf_printf(out, "    \"min\":       %llu,\n", stats->min_duration);
> +	seq_buf_printf(out, "    \"max\":       %llu,\n", stats->max_duration);
> +	seq_buf_printf(out, "    \"total\":     %llu,\n", stats->total_duration);
> +	seq_buf_printf(out, "    \"mean\":      %llu,\n", d_mean);
> +	seq_buf_printf(out, "    \"stddev\":    %llu\n", d_stddev);
> +	seq_buf_printf(out, "  },\n");
> +
> +	d_mean = mean_and_variance_weighted_get_mean(stats->duration_stats_weighted, TIME_STATS_MV_WEIGHT);
> +	d_stddev = mean_and_variance_weighted_get_stddev(stats->duration_stats_weighted, TIME_STATS_MV_WEIGHT);
> +
> +	seq_buf_printf(out, "  \"duration_ewma_ns\": {\n");
> +	seq_buf_printf(out, "    \"mean\":      %llu,\n", d_mean);
> +	seq_buf_printf(out, "    \"stddev\":    %llu\n", d_stddev);
> +	seq_buf_printf(out, "  },\n");
> +
> +	seq_buf_printf(out, "  \"frequency_ns\": {\n");

I took the variable names too literally here; these labels really ought
to be "between_ns" and "between_ewma_ns" to maintain consistency with
the labels in the table format.

> +	seq_buf_printf(out, "    \"min\":       %llu,\n", stats->min_freq);
> +	seq_buf_printf(out, "    \"max\":       %llu,\n", stats->max_freq);
> +	seq_buf_printf(out, "    \"mean\":      %llu,\n", f_mean);
> +	seq_buf_printf(out, "    \"stddev\":    %llu\n", f_stddev);
> +	seq_buf_printf(out, "  },\n");
> +
> +	f_mean = mean_and_variance_weighted_get_mean(stats->freq_stats_weighted, TIME_STATS_MV_WEIGHT);
> +	f_stddev = mean_and_variance_weighted_get_stddev(stats->freq_stats_weighted, TIME_STATS_MV_WEIGHT);
> +
> +	seq_buf_printf(out, "  \"frequency_ewma_ns\": {\n");
> +	seq_buf_printf(out, "    \"mean\":      %llu,\n", f_mean);
> +	seq_buf_printf(out, "    \"stddev\":    %llu\n", f_stddev);
> +
> +	if (quantiles) {
> +		u64 last_q = 0;
> +
> +		/* close frequency_ewma_ns but signal more items */

(also this comment)

> +		seq_buf_printf(out, "  },\n");
> +
> +		seq_buf_printf(out, "  \"quantiles_ns\": [\n");
> +		eytzinger0_for_each(i, NR_QUANTILES) {
> +			bool is_last = eytzinger0_next(i, NR_QUANTILES) == -1;
> +
> +			u64 q = max(quantiles->entries[i].m, last_q);
> +			seq_buf_printf(out, "    %llu", q);
> +			if (!is_last)
> +				seq_buf_printf(out, ", ");
> +			last_q = q;
> +		}
> +		seq_buf_printf(out, "  ]\n");
> +	} else {
> +		/* close frequency_ewma_ns without dumping further */

(this one too)

Kent, would you mind making that edit the next time you reflow your
branch?

--D

> +		seq_buf_printf(out, "  }\n");
> +	}
> +
> +	seq_buf_printf(out, "}\n");
> +}
> +EXPORT_SYMBOL_GPL(time_stats_to_json);
> +
>  void time_stats_exit(struct time_stats *stats)
>  {
>  	free_percpu(stats->buffer);
> 
>