linux-kernel - Re: [PATCH] Add the latency-collector to tools

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Date:   Thu, 11 Feb 2021 14:56:48 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Viktor Rosendahl <Viktor.Rosendahl@....de>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add the latency-collector to tools

On Thu, 11 Feb 2021 17:17:42 +0100
Viktor Rosendahl <Viktor.Rosendahl@....de> wrote:

> It seems to work but I discovered during testing that it seems like newer
> kernels have a tendency to lose some latencies in longer bursts. I guess this
> is likely to be another regression in the preemptirqsoff tracer.

Not sure what you mean by the above. I'd be interested in fixing it if is
really a problem.

> diff --git a/tools/tracing/Makefile b/tools/tracing/Makefile
> new file mode 100644
> index 000000000000..f53859765154
> --- /dev/null
> +++ b/tools/tracing/Makefile
> @@ -0,0 +1,23 @@
> +# SPDX-License-Identifier: GPL-2.0
> +# Makefile for vm tools
> +#
> +VAR_CFLAGS := $(shell pkg-config --cflags libtracefs 2>/dev/null)
> +VAR_LDLIBS := $(shell pkg-config --libs libtracefs 2>/dev/null)
> +
> +TARGETS = latency-collector
> +CFLAGS = -Wall -Wextra -g -O2 $(VAR_CFLAGS)
> +LDFLAGS = -lpthread $(VAR_LDLIBS)
> +
> +all: $(TARGETS)
> +
> +%: %.c
> +	$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
> +
> +clean:
> +	$(RM) latency-collector
> +
> +sbindir ?= /usr/sbin

I wonder if it should default to /usr/local?

 prefix ?= /usr/local
 sbindir ?= ${prefix}/sbin

> +
> +install: all
> +	install -d $(DESTDIR)$(sbindir)
> +	install -m 755 -p $(TARGETS) $(DESTDIR)$(sbindir)
> diff --git a/tools/tracing/latency-collector.c b/tools/tracing/latency-collector.c
> new file mode 100644
> index 000000000000..e9aa7a47a8a3
> --- /dev/null
> +++ b/tools/tracing/latency-collector.c
> @@ -0,0 +1,2102 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2017, 2018, 2019, 2021 BMW Car IT GmbH
> + * Author: Viktor Rosendahl (viktor.rosendahl@....de)
> + */
> +
> +#define _GNU_SOURCE
> +#define _POSIX_C_SOURCE 200809L
> +
> +#include <ctype.h>
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +
> +#include <err.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <getopt.h>
> +#include <sched.h>
> +#include <linux/unistd.h>
> +#include <signal.h>
> +#include <sys/inotify.h>
> +#include <unistd.h>
> +#include <pthread.h>
> +#include <tracefs.h>
> +
> +static const char *prg_name;
> +static const char *prg_unknown = "unknown program name";
> +
> +static int fd_stdout;
> +
> +static int sched_policy;
> +static bool sched_policy_set;
> +
> +static int sched_pri;
> +static bool sched_pri_set;
> +
> +static bool trace_enable = true;
> +static bool setup_ftrace = true;
> +static bool use_random_sleep;
> +
> +enum traceopt {
> +	OPTIDX_FUNC_TR = 0,
> +	OPTIDX_DISP_GR,
> +	OPTIDX_NR
> +};
> +
> +/* Should be in the order of enum traceopt */
> +static  const char * const optstr[] = {
> +	"function-trace", /* OPTIDX_FUNC_TR  */
> +	"display-graph",  /* OPTIDX_DISP_GR  */
> +	NULL
> +};

A trick to force the enum and string order is this:


#define TRACE_OPTS		\
  C(FUNC_TR, "function-trace"),	\
  C(DISP_GR, "display-graph")

#undef C
#define C(a, b) OPTIDX_##a

enum traceopt {
	TRACE_OPTS,
	OPTIDX_NR
};

#undef C
#define C(a, b)  b

static const char *cost optstr[] = {
	TRACE_OPTS,
	NULL
};


> +
> +enum errhandling {
> +	ERR_EXIT = 0,
> +	ERR_WARN,
> +	ERR_CLEANUP,
> +};

I didn't look too deeply at the rest, just skimmed it basically, and I
tried it out.

I'm fine with pulling this into my queue, as it's just a tool and wont
cause any other issues. I can move some of the files in scripts that deals
with tracing into the tools/tracing directory too. Maybe this should be
placed in a sub directory? tools/tracing/latency/ ?

Feel free to submit a proper patch (proper change log, etc).

Thanks,

-- Steve