[LTP] [PATCH v1] Correctly handle user time in setitimer01

[Cyril Hrubis]

Hi!
> Since ITIMER_VIRTUAL and ITIMER_PROF are counting down in user time, we
> need to take in consideration CLOCK_MONOTONIC_COARSE resolution. This is
> requested by the syscall, since it's considering context switch from
> user to kernel mode by using a higher clock resolution.

What exactly do you mean by this? I do not think that there is "user"
and "kernel" time, just different in-kernel timers/counters with
different precisions.

As ITIMER_VIRTUAL and ITIMER_PROF counts CPU time the precision would be
the same as the COARSE clocks which depends on jiffies and on the
compile time option CONFIG_HZ. That is because in the scheduller the CPU
time is quantized into chunks based on CONFIG_HZ.

And the ITIMER_REAL runs on hrtimers which would be the same precision
as CLOCK_REALTIME or CLOCK_MONOTONIC.

> Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
> ---
>  .../kernel/syscalls/setitimer/setitimer01.c   | 54 +++++++++++--------
>  1 file changed, 33 insertions(+), 21 deletions(-)
> 
> diff --git a/testcases/kernel/syscalls/setitimer/setitimer01.c b/testcases/kernel/syscalls/setitimer/setitimer01.c
> index eb62f02c6..5fcae53e8 100644
> --- a/testcases/kernel/syscalls/setitimer/setitimer01.c
> +++ b/testcases/kernel/syscalls/setitimer/setitimer01.c
> @@ -8,9 +8,16 @@
>  /*\
>   * [Description]
>   *
> - * Spawn a child and verify that setitimer() syscall passes, and it ends up
> + * Spawn a child, verify that setitimer() syscall passes and it ends up
>   * counting inside expected boundaries. Then verify from the parent that our
>   * syscall sent the correct signal to the child.
> + *
> + * Boundaries are choosen accordingly with system clock. In particular, when
> + * timer counts down in real time, CLOCK_MONOTONIC resolution has taken into
> + * account as our time step. When timer counts down in user time,
> + * CLOCK_MONOTONIC_COARSE is used. The reason is that CLOCK_MONOTONIC_COARSE
> + * is our system resolution in user space, since it's taking in consideration
> + * context switches from user to kernel space.
>   */
>  
>  #include <time.h>
> @@ -22,7 +29,6 @@
>  #include "tst_safe_clocks.h"
>  
>  static struct itimerval *value, *ovalue;
> -static unsigned long time_step;
>  
>  static struct tcase {
>  	int which;
> @@ -55,9 +61,31 @@ static void set_setitimer_value(int usec, int o_usec)
>  static void verify_setitimer(unsigned int i)
>  {
>  	pid_t pid;
> -	int status;
> -	int usec = 3 * time_step;
> +	struct timespec res;
>  	struct tcase *tc = &tcases[i];
> +	int status, usec, time_step, error;
> +
> +	if (tc->which == ITIMER_REAL)
> +		SAFE_CLOCK_GETRES(CLOCK_MONOTONIC, &res);
> +	else
> +		SAFE_CLOCK_GETRES(CLOCK_MONOTONIC_COARSE, &res);

This is not going to change, so we may as well get the fine/coarse
resolution once in the test setup and initialize fine/coarse time step
once as well.

> +	time_step = res.tv_nsec / 1000;
> +	error = time_step;
> +
> +	if (time_step <= 0) {
> +		time_step = 1000;
> +		error = 0;
> +	}
> +
> +	usec = 3 * time_step;
> +
> +	tst_res(TINFO, "clock resolution: %luns, "
> +		"time step: %ius, "
> +		"counter time: %ius",
> +		res.tv_nsec,
> +		time_step,
> +		usec);
>  
>  	pid = SAFE_FORK();
>  
> @@ -76,7 +104,7 @@ static void verify_setitimer(unsigned int i)
>  			ovalue->it_value.tv_sec,
>  			ovalue->it_value.tv_usec);
>  
> -		if (ovalue->it_value.tv_sec != 0 || ovalue->it_value.tv_usec > usec)
> +		if (ovalue->it_value.tv_sec != 0 || ovalue->it_value.tv_usec > usec + error)
>  			tst_res(TFAIL, "Ending counters are out of range");
>  
>  		for (;;)
> @@ -91,26 +119,10 @@ static void verify_setitimer(unsigned int i)
>  		tst_res(TFAIL, "Child: %s", tst_strstatus(status));
>  }
>  
> -static void setup(void)
> -{
> -	struct timespec res;
> -
> -	SAFE_CLOCK_GETRES(CLOCK_MONOTONIC, &res);
> -
> -	time_step = res.tv_nsec / 1000;
> -	if (time_step < 10000)
> -		time_step = 10000;
> -
> -	tst_res(TINFO, "clock resolution: %luns, time step: %luus",
> -		res.tv_nsec,
> -		time_step);
> -}
> -
>  static struct tst_test test = {
>  	.tcnt = ARRAY_SIZE(tcases),
>  	.forks_child = 1,
>  	.test = verify_setitimer,
> -	.setup = setup,
>  	.bufs = (struct tst_buffers[]) {
>  		{&value,  .size = sizeof(struct itimerval)},
>  		{&ovalue, .size = sizeof(struct itimerval)},
> -- 
> 2.35.3
> 
> 
> -- 
> Mailing list info: https://lists.linux.it/listinfo/ltp

-- 
Cyril Hrubis
chrubis@suse.cz