linux-kernel - Re: [PATCH v5 6/8] perf report: Add --latency flag

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Message-ID: <Z6WDsmeVr7qPk0te@google.com>
Date: Thu, 6 Feb 2025 19:53:22 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: irogers@...gle.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH v5 6/8] perf report: Add --latency flag

On Wed, Feb 05, 2025 at 05:27:45PM +0100, Dmitry Vyukov wrote:
> Add record/report --latency flag that allows to capture and show
> latency-centric profiles rather than the default CPU-consumption-centric
> profiles. For latency profiles record captures context switch events,
> and report shows Latency as the first column.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: linux-perf-users@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> 
> ---
[SNIP]  
> +void perf_hpp__cancel_latency(void)
> +{
> +	struct perf_hpp_fmt *fmt, *lat, *acc, *tmp;
> +
> +	if (is_strict_order(field_order) || is_strict_order(sort_order))
> +		return;

This also needs to be changed since you call setup_overhead even if you
have a strict sort_order.

For example, it's strange these two are different.

With default sort order:

  $ perf record --latency -- ls /

  $ perf report --stdio
  ...
  # Overhead  Command  Shared Object         Symbol                  
  # ........  .......  ....................  ........................
  #
      64.50%  ls       ld-linux-x86-64.so.2  [.] do_lookup_x
      33.41%  ls       [kernel.kallsyms]     [k] chacha_block_generic
       2.00%  perf-ex  [kernel.kallsyms]     [k] put_ctx
       0.09%  perf-ex  [kernel.kallsyms]     [k] native_write_msr
  
Same sort order, but explicitly:

  $ perf report --stdio -s comm,dso,sym
  ...
  # Overhead   Latency  Command  Shared Object         Symbol                  
  # ........  ........  .......  ....................  ........................
  #
      64.50%    64.50%  ls       ld-linux-x86-64.so.2  [.] do_lookup_x
      33.41%    33.41%  ls       [kernel.kallsyms]     [k] chacha_block_generic
       2.00%     2.00%  perf-ex  [kernel.kallsyms]     [k] put_ctx
       0.09%     0.09%  perf-ex  [kernel.kallsyms]     [k] native_write_msr

Maybe you want to cancel the latency field even if sort key is given
(unless it has 'latency').

Something like this?

---8<---
@@ -714,7 +715,9 @@ void perf_hpp__cancel_latency(void)
 {
        struct perf_hpp_fmt *fmt, *lat, *acc, *tmp;
 
-       if (is_strict_order(field_order) || is_strict_order(sort_order))
+       if (is_strict_order(field_order))
+               return;
+       if (is_strict_order(sort_order) && strstr(sort_order, "latency"))
                return;
 
        lat = &perf_hpp__format[PERF_HPP__LATENCY];
---8<---

Thanks,
Namhyung

> +
> +	lat = &perf_hpp__format[PERF_HPP__LATENCY];
> +	acc = &perf_hpp__format[PERF_HPP__LATENCY_ACC];
> +
> +	perf_hpp_list__for_each_format_safe(&perf_hpp_list, fmt, tmp) {
> +		if (fmt_equal(lat, fmt) || fmt_equal(acc, fmt))
> +			perf_hpp__column_unregister(fmt);
> +	}
> +}
> +
>  void perf_hpp__setup_output_field(struct perf_hpp_list *list)
>  {
>  	struct perf_hpp_fmt *fmt;