diff mbox series

perf stat: Do not delay the workload with --delay

Message ID	20221212230820.901382-1-namhyung@kernel.org
State	New
Headers	Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Sender: Namhyung Kim <namhyung@gmail.com> From: Namhyung Kim <namhyung@kernel.org> To: Arnaldo Carvalho de Melo <acme@kernel.org>, Jiri Olsa <jolsa@kernel.org> Cc: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>, LKML <linux-kernel@vger.kernel.org>, Ian Rogers <irogers@google.com>, Adrian Hunter <adrian.hunter@intel.com>, linux-perf-users@vger.kernel.org, Sumanth Korikkar <sumanthk@linux.ibm.com>, Thomas Richter <tmricht@linux.ibm.com>, Kevin Nomura <nomurak@google.com> Subject: [PATCH] perf stat: Do not delay the workload with --delay Date: Mon, 12 Dec 2022 15:08:20 -0800 Message-Id: <20221212230820.901382-1-namhyung@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk
Series	perf stat: Do not delay the workload with --delay \| perf stat: Do not delay the workload with --delay

Commit Message

Namhyung Kim Dec. 12, 2022, 11:08 p.m. UTC

  The -D/--delay option is to delay the measure after the program starts.
But the current code goes to sleep before starting the program so the
program is delayed too.  This is not the intention, let's fix it.

Before:

  $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
  Events disabled
  Events enabled

   Performance counter stats for 'system wide':

       4,326,949,337      cycles

         4.007494118 seconds time elapsed

  real	0m7.474s
  user	0m0.356s
  sys	0m0.120s

It ran the workload for 4 seconds and gave the 3 second delay.  So it
should skip the first 3 second and measure the last 1 second only.  But
as you can see, it delays 3 seconds and ran the workload after that for
4 seconds.  So the total time (real) was 7 seconds.

After:

  $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
  Events disabled
  Events enabled

   Performance counter stats for 'system wide':

       1,063,551,013      cycles

         1.002769510 seconds time elapsed

  real	0m4.484s
  user	0m0.385s
  sys	0m0.086s

The bug was introduced when it changed enablement of system-wide events
with a command line workload.  But it should've considered the initial
delay case.  The code was reworked since then (in bb8bc52e7578) so I'm
afraid it won't be applied cleanly.

Fixes: d0a0a511493d ("perf stat: Fix forked applications enablement of counters")
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Reported-by: Kevin Nomura <nomurak@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/builtin-stat.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

Comments

Thomas Richter Dec. 13, 2022, 1:13 p.m. UTC | #1

On 12/13/22 00:08, Namhyung Kim wrote:
> The -D/--delay option is to delay the measure after the program starts.
> But the current code goes to sleep before starting the program so the
> program is delayed too.  This is not the intention, let's fix it.
> 
> Before:
> 
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
> 
>    Performance counter stats for 'system wide':
> 
>        4,326,949,337      cycles
> 
>          4.007494118 seconds time elapsed
> 
>   real	0m7.474s
>   user	0m0.356s
>   sys	0m0.120s
> 
> It ran the workload for 4 seconds and gave the 3 second delay.  So it
> should skip the first 3 second and measure the last 1 second only.  But
> as you can see, it delays 3 seconds and ran the workload after that for
> 4 seconds.  So the total time (real) was 7 seconds.
> 
> After:
> 
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
> 
>    Performance counter stats for 'system wide':
> 
>        1,063,551,013      cycles
> 
>          1.002769510 seconds time elapsed
> 
>   real	0m4.484s
>   user	0m0.385s
>   sys	0m0.086s
> 
> The bug was introduced when it changed enablement of system-wide events
> with a command line workload.  But it should've considered the initial
> delay case.  The code was reworked since then (in bb8bc52e7578) so I'm
> afraid it won't be applied cleanly.
> 
> Fixes: d0a0a511493d ("perf stat: Fix forked applications enablement of counters")
> Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
> Cc: Thomas Richter <tmricht@linux.ibm.com>
> Reported-by: Kevin Nomura <nomurak@google.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/builtin-stat.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index d040fbcdcc5a..b39bf785a16e 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -540,26 +540,14 @@ static int enable_counters(void)
>  			return err;
>  	}
>  
> -	if (stat_config.initial_delay < 0) {
> -		pr_info(EVLIST_DISABLED_MSG);
> -		return 0;
> -	}
> -
> -	if (stat_config.initial_delay > 0) {
> -		pr_info(EVLIST_DISABLED_MSG);
> -		usleep(stat_config.initial_delay * USEC_PER_MSEC);
> -	}
> -
>  	/*
>  	 * We need to enable counters only if:
>  	 * - we don't have tracee (attaching to task or cpu)
>  	 * - we have initial delay configured
>  	 */
> -	if (!target__none(&target) || stat_config.initial_delay) {
> +	if (!target__none(&target)) {
>  		if (!all_counters_use_bpf)
>  			evlist__enable(evsel_list);
> -		if (stat_config.initial_delay > 0)
> -			pr_info(EVLIST_ENABLED_MSG);
>  	}
>  	return 0;
>  }
> @@ -930,14 +918,27 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>  			return err;
>  	}
>  
> -	err = enable_counters();
> -	if (err)
> -		return -1;
> +	if (stat_config.initial_delay) {
> +		pr_info(EVLIST_DISABLED_MSG);
> +	} else {
> +		err = enable_counters();
> +		if (err)
> +			return -1;
> +	}
>  
>  	/* Exec the command, if any */
>  	if (forks)
>  		evlist__start_workload(evsel_list);
>  
> +	if (stat_config.initial_delay > 0) {
> +		usleep(stat_config.initial_delay * USEC_PER_MSEC);
> +		err = enable_counters();
> +		if (err)
> +			return -1;
> +
> +		pr_info(EVLIST_ENABLED_MSG);
> +	}
> +
>  	t0 = rdclock();
>  	clock_gettime(CLOCK_MONOTONIC, &ref_time);
>  

Tested successfully on s390

Acked-by: Thomas Richter <tmricht@linux.ibm.com>

James Clark Dec. 13, 2022, 1:39 p.m. UTC | #2

On 12/12/2022 23:08, Namhyung Kim wrote:
> The -D/--delay option is to delay the measure after the program starts.
> But the current code goes to sleep before starting the program so the
> program is delayed too.  This is not the intention, let's fix it.
> 
> Before:
> 
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
> 
>    Performance counter stats for 'system wide':
> 
>        4,326,949,337      cycles
> 
>          4.007494118 seconds time elapsed
> 
>   real	0m7.474s
>   user	0m0.356s
>   sys	0m0.120s
> 
> It ran the workload for 4 seconds and gave the 3 second delay.  So it
> should skip the first 3 second and measure the last 1 second only.  But
> as you can see, it delays 3 seconds and ran the workload after that for
> 4 seconds.  So the total time (real) was 7 seconds.
> 
> After:
> 
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
> 
>    Performance counter stats for 'system wide':
> 
>        1,063,551,013      cycles
> 
>          1.002769510 seconds time elapsed
> 
>   real	0m4.484s
>   user	0m0.385s
>   sys	0m0.086s
> 
> The bug was introduced when it changed enablement of system-wide events
> with a command line workload.  But it should've considered the initial
> delay case.  The code was reworked since then (in bb8bc52e7578) so I'm
> afraid it won't be applied cleanly.
> 
> Fixes: d0a0a511493d ("perf stat: Fix forked applications enablement of counters")

Looks like the same fix as here, but it was only partially applied:

https://lore.kernel.org/linux-perf-users/20220801112726.GA73228@leoy-ThinkPad-X240s/T/#mce4ad6b17a5fa15970765bb01e7b691c7326fbb0


> Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
> Cc: Thomas Richter <tmricht@linux.ibm.com>
> Reported-by: Kevin Nomura <nomurak@google.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/builtin-stat.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index d040fbcdcc5a..b39bf785a16e 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -540,26 +540,14 @@ static int enable_counters(void)
>  			return err;
>  	}
>  
> -	if (stat_config.initial_delay < 0) {
> -		pr_info(EVLIST_DISABLED_MSG);
> -		return 0;
> -	}
> -
> -	if (stat_config.initial_delay > 0) {
> -		pr_info(EVLIST_DISABLED_MSG);
> -		usleep(stat_config.initial_delay * USEC_PER_MSEC);
> -	}
> -
>  	/*
>  	 * We need to enable counters only if:
>  	 * - we don't have tracee (attaching to task or cpu)
>  	 * - we have initial delay configured
>  	 */
> -	if (!target__none(&target) || stat_config.initial_delay) {
> +	if (!target__none(&target)) {
>  		if (!all_counters_use_bpf)
>  			evlist__enable(evsel_list);
> -		if (stat_config.initial_delay > 0)
> -			pr_info(EVLIST_ENABLED_MSG);
>  	}
>  	return 0;
>  }
> @@ -930,14 +918,27 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>  			return err;
>  	}
>  
> -	err = enable_counters();
> -	if (err)
> -		return -1;
> +	if (stat_config.initial_delay) {
> +		pr_info(EVLIST_DISABLED_MSG);
> +	} else {
> +		err = enable_counters();
> +		if (err)
> +			return -1;
> +	}
>  
>  	/* Exec the command, if any */
>  	if (forks)
>  		evlist__start_workload(evsel_list);
>  
> +	if (stat_config.initial_delay > 0) {
> +		usleep(stat_config.initial_delay * USEC_PER_MSEC);
> +		err = enable_counters();
> +		if (err)
> +			return -1;
> +
> +		pr_info(EVLIST_ENABLED_MSG);
> +	}
> +
>  	t0 = rdclock();
>  	clock_gettime(CLOCK_MONOTONIC, &ref_time);
>

Ian Rogers Dec. 14, 2022, 12:18 a.m. UTC | #3

On Mon, Dec 12, 2022 at 3:08 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> The -D/--delay option is to delay the measure after the program starts.
> But the current code goes to sleep before starting the program so the
> program is delayed too.  This is not the intention, let's fix it.
>
> Before:
>
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
>
>    Performance counter stats for 'system wide':
>
>        4,326,949,337      cycles
>
>          4.007494118 seconds time elapsed
>
>   real  0m7.474s
>   user  0m0.356s
>   sys   0m0.120s
>
> It ran the workload for 4 seconds and gave the 3 second delay.  So it
> should skip the first 3 second and measure the last 1 second only.  But
> as you can see, it delays 3 seconds and ran the workload after that for
> 4 seconds.  So the total time (real) was 7 seconds.
>
> After:
>
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
>
>    Performance counter stats for 'system wide':
>
>        1,063,551,013      cycles
>
>          1.002769510 seconds time elapsed
>
>   real  0m4.484s
>   user  0m0.385s
>   sys   0m0.086s

The commit message feels like it could almost be turned into a shell
test. The test would need some fudge factors in case of load on the
test system. Any thoughts if we could add this? We wouldn't need to
rely on 'time' as we have tool events of user_time, system_time, etc.

Thanks,
Ian

> The bug was introduced when it changed enablement of system-wide events
> with a command line workload.  But it should've considered the initial
> delay case.  The code was reworked since then (in bb8bc52e7578) so I'm
> afraid it won't be applied cleanly.
>
> Fixes: d0a0a511493d ("perf stat: Fix forked applications enablement of counters")
> Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
> Cc: Thomas Richter <tmricht@linux.ibm.com>
> Reported-by: Kevin Nomura <nomurak@google.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/builtin-stat.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index d040fbcdcc5a..b39bf785a16e 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -540,26 +540,14 @@ static int enable_counters(void)
>                         return err;
>         }
>
> -       if (stat_config.initial_delay < 0) {
> -               pr_info(EVLIST_DISABLED_MSG);
> -               return 0;
> -       }
> -
> -       if (stat_config.initial_delay > 0) {
> -               pr_info(EVLIST_DISABLED_MSG);
> -               usleep(stat_config.initial_delay * USEC_PER_MSEC);
> -       }
> -
>         /*
>          * We need to enable counters only if:
>          * - we don't have tracee (attaching to task or cpu)
>          * - we have initial delay configured
>          */
> -       if (!target__none(&target) || stat_config.initial_delay) {
> +       if (!target__none(&target)) {
>                 if (!all_counters_use_bpf)
>                         evlist__enable(evsel_list);
> -               if (stat_config.initial_delay > 0)
> -                       pr_info(EVLIST_ENABLED_MSG);
>         }
>         return 0;
>  }
> @@ -930,14 +918,27 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>                         return err;
>         }
>
> -       err = enable_counters();
> -       if (err)
> -               return -1;
> +       if (stat_config.initial_delay) {
> +               pr_info(EVLIST_DISABLED_MSG);
> +       } else {
> +               err = enable_counters();
> +               if (err)
> +                       return -1;
> +       }
>
>         /* Exec the command, if any */
>         if (forks)
>                 evlist__start_workload(evsel_list);
>
> +       if (stat_config.initial_delay > 0) {
> +               usleep(stat_config.initial_delay * USEC_PER_MSEC);
> +               err = enable_counters();
> +               if (err)
> +                       return -1;
> +
> +               pr_info(EVLIST_ENABLED_MSG);
> +       }
> +
>         t0 = rdclock();
>         clock_gettime(CLOCK_MONOTONIC, &ref_time);
>
> --
> 2.39.0.rc1.256.g54fd8350bd-goog
>

Arnaldo Carvalho de Melo Dec. 14, 2022, 2:41 p.m. UTC | #4

Em Mon, Dec 12, 2022 at 03:08:20PM -0800, Namhyung Kim escreveu:
> The -D/--delay option is to delay the measure after the program starts.
> But the current code goes to sleep before starting the program so the
> program is delayed too.  This is not the intention, let's fix it.
> 
> Before:
> 
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
> 
>    Performance counter stats for 'system wide':
> 
>        4,326,949,337      cycles
> 
>          4.007494118 seconds time elapsed
> 
>   real	0m7.474s
>   user	0m0.356s
>   sys	0m0.120s
> 
> It ran the workload for 4 seconds and gave the 3 second delay.  So it
> should skip the first 3 second and measure the last 1 second only.  But
> as you can see, it delays 3 seconds and ran the workload after that for
> 4 seconds.  So the total time (real) was 7 seconds.
> 
> After:
> 
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
> 
>    Performance counter stats for 'system wide':
> 
>        1,063,551,013      cycles
> 
>          1.002769510 seconds time elapsed
> 
>   real	0m4.484s
>   user	0m0.385s
>   sys	0m0.086s
> 
> The bug was introduced when it changed enablement of system-wide events
> with a command line workload.  But it should've considered the initial
> delay case.  The code was reworked since then (in bb8bc52e7578) so I'm
> afraid it won't be applied cleanly.

Ok, I took up this one instead of Adrian's.

- Arnaldo
 
> Fixes: d0a0a511493d ("perf stat: Fix forked applications enablement of counters")
> Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
> Cc: Thomas Richter <tmricht@linux.ibm.com>
> Reported-by: Kevin Nomura <nomurak@google.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/builtin-stat.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index d040fbcdcc5a..b39bf785a16e 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -540,26 +540,14 @@ static int enable_counters(void)
>  			return err;
>  	}
>  
> -	if (stat_config.initial_delay < 0) {
> -		pr_info(EVLIST_DISABLED_MSG);
> -		return 0;
> -	}
> -
> -	if (stat_config.initial_delay > 0) {
> -		pr_info(EVLIST_DISABLED_MSG);
> -		usleep(stat_config.initial_delay * USEC_PER_MSEC);
> -	}
> -
>  	/*
>  	 * We need to enable counters only if:
>  	 * - we don't have tracee (attaching to task or cpu)
>  	 * - we have initial delay configured
>  	 */
> -	if (!target__none(&target) || stat_config.initial_delay) {
> +	if (!target__none(&target)) {
>  		if (!all_counters_use_bpf)
>  			evlist__enable(evsel_list);
> -		if (stat_config.initial_delay > 0)
> -			pr_info(EVLIST_ENABLED_MSG);
>  	}
>  	return 0;
>  }
> @@ -930,14 +918,27 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>  			return err;
>  	}
>  
> -	err = enable_counters();
> -	if (err)
> -		return -1;
> +	if (stat_config.initial_delay) {
> +		pr_info(EVLIST_DISABLED_MSG);
> +	} else {
> +		err = enable_counters();
> +		if (err)
> +			return -1;
> +	}
>  
>  	/* Exec the command, if any */
>  	if (forks)
>  		evlist__start_workload(evsel_list);
>  
> +	if (stat_config.initial_delay > 0) {
> +		usleep(stat_config.initial_delay * USEC_PER_MSEC);
> +		err = enable_counters();
> +		if (err)
> +			return -1;
> +
> +		pr_info(EVLIST_ENABLED_MSG);
> +	}
> +
>  	t0 = rdclock();
>  	clock_gettime(CLOCK_MONOTONIC, &ref_time);
>  
> -- 
> 2.39.0.rc1.256.g54fd8350bd-goog

Leo Yan Dec. 15, 2022, 1:43 a.m. UTC | #5

On Mon, Dec 12, 2022 at 03:08:20PM -0800, Namhyung Kim wrote:
> The -D/--delay option is to delay the measure after the program starts.
> But the current code goes to sleep before starting the program so the
> program is delayed too.  This is not the intention, let's fix it.
> 
> Before:
> 
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
> 
>    Performance counter stats for 'system wide':
> 
>        4,326,949,337      cycles
> 
>          4.007494118 seconds time elapsed
> 
>   real	0m7.474s
>   user	0m0.356s
>   sys	0m0.120s
> 
> It ran the workload for 4 seconds and gave the 3 second delay.  So it
> should skip the first 3 second and measure the last 1 second only.  But
> as you can see, it delays 3 seconds and ran the workload after that for
> 4 seconds.  So the total time (real) was 7 seconds.
> 
> After:
> 
>   $ time sudo ./perf stat -a -e cycles -D 3000 sleep 4
>   Events disabled
>   Events enabled
> 
>    Performance counter stats for 'system wide':
> 
>        1,063,551,013      cycles
> 
>          1.002769510 seconds time elapsed
> 
>   real	0m4.484s
>   user	0m0.385s
>   sys	0m0.086s
> 
> The bug was introduced when it changed enablement of system-wide events
> with a command line workload.  But it should've considered the initial
> delay case.  The code was reworked since then (in bb8bc52e7578) so I'm
> afraid it won't be applied cleanly.
> 
> Fixes: d0a0a511493d ("perf stat: Fix forked applications enablement of counters")
> Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
> Cc: Thomas Richter <tmricht@linux.ibm.com>
> Reported-by: Kevin Nomura <nomurak@google.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Reviewed-by: Leo Yan <leo.yan@linaro.org>

diff mbox series

Patch

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index d040fbcdcc5a..b39bf785a16e 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -540,26 +540,14 @@  static int enable_counters(void)
 			return err;
 	}
 
-	if (stat_config.initial_delay < 0) {
-		pr_info(EVLIST_DISABLED_MSG);
-		return 0;
-	}
-
-	if (stat_config.initial_delay > 0) {
-		pr_info(EVLIST_DISABLED_MSG);
-		usleep(stat_config.initial_delay * USEC_PER_MSEC);
-	}
-
 	/*
 	 * We need to enable counters only if:
 	 * - we don't have tracee (attaching to task or cpu)
 	 * - we have initial delay configured
 	 */
-	if (!target__none(&target) || stat_config.initial_delay) {
+	if (!target__none(&target)) {
 		if (!all_counters_use_bpf)
 			evlist__enable(evsel_list);
-		if (stat_config.initial_delay > 0)
-			pr_info(EVLIST_ENABLED_MSG);
 	}
 	return 0;
 }
@@ -930,14 +918,27 @@  static int __run_perf_stat(int argc, const char **argv, int run_idx)
 			return err;
 	}
 
-	err = enable_counters();
-	if (err)
-		return -1;
+	if (stat_config.initial_delay) {
+		pr_info(EVLIST_DISABLED_MSG);
+	} else {
+		err = enable_counters();
+		if (err)
+			return -1;
+	}
 
 	/* Exec the command, if any */
 	if (forks)
 		evlist__start_workload(evsel_list);
 
+	if (stat_config.initial_delay > 0) {
+		usleep(stat_config.initial_delay * USEC_PER_MSEC);
+		err = enable_counters();
+		if (err)
+			return -1;
+
+		pr_info(EVLIST_ENABLED_MSG);
+	}
+
 	t0 = rdclock();
 	clock_gettime(CLOCK_MONOTONIC, &ref_time);