Re: [PATCH v2 3/6] rtla/utils: Add idle state disabling via libcpupower

[Steven Rostedt]

On Wed, 31 Jul 2024 10:36:52 +0200
tglozar@xxxxxxxxxx wrote:

> From: Tomas Glozar <tglozar@xxxxxxxxxx>
> 
> Add functions to utils.c to disable idle states through functions of
> libcpupower. This will serve as the basis for disabling idle states
> per cpu when running timerlat.
> 
> Signed-off-by: Tomas Glozar <tglozar@xxxxxxxxxx>
> ---
>  tools/tracing/rtla/src/utils.c | 140 +++++++++++++++++++++++++++++++++
>  tools/tracing/rtla/src/utils.h |   6 ++
>  2 files changed, 146 insertions(+)
> 
> diff --git a/tools/tracing/rtla/src/utils.c b/tools/tracing/rtla/src/utils.c
> index 9ac71a66840c..9279b8ce08c3 100644
> --- a/tools/tracing/rtla/src/utils.c
> +++ b/tools/tracing/rtla/src/utils.c
> @@ -4,6 +4,9 @@
>   */
>  
>  #define _GNU_SOURCE
> +#ifdef HAVE_LIBCPUPOWER_SUPPORT
> +#include <cpuidle.h>
> +#endif /* HAVE_LIBCPUPOWER_SUPPORT */
>  #include <dirent.h>
>  #include <stdarg.h>
>  #include <stdlib.h>
> @@ -519,6 +522,143 @@ int set_cpu_dma_latency(int32_t latency)
>  	return fd;
>  }
>  
> +#ifdef HAVE_LIBCPUPOWER_SUPPORT
> +static unsigned int **saved_cpu_idle_disable_state;
> +static size_t saved_cpu_idle_disable_state_alloc_ctr;
> +
> +/*
> + * save_cpu_idle_state_disable - save disable for all idle states of a cpu
> + *
> + * Saves the current disable of all idle states of a cpu, to be subsequently
> + * restored via restore_cpu_idle_disable_state.
> + *
> + * Return: idle state count on success, negative on error
> + */
> +int save_cpu_idle_disable_state(unsigned int cpu)
> +{
> +	unsigned int nr_states;
> +	unsigned int state;
> +	int disabled;
> +	int nr_cpus;
> +
> +	nr_states = cpuidle_state_count(cpu);
> +
> +	if (nr_states == 0)
> +		return 0;
> +
> +	if (saved_cpu_idle_disable_state == NULL) {
> +		nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
> +		saved_cpu_idle_disable_state = calloc(nr_cpus, sizeof(unsigned int *));

Need to check if the calloc failed and return an error if it did.

> +	}
> +
> +	saved_cpu_idle_disable_state[cpu] = calloc(nr_states, sizeof(unsigned int));

Here too.

> +	saved_cpu_idle_disable_state_alloc_ctr++;
> +
> +	for (state = 0; state < nr_states; state++) {
> +		disabled = cpuidle_is_state_disabled(cpu, state);
> +		if (disabled < 0)
> +			return disabled;

Hmm, should this warn if state is not zero and disabled is negative.

> +		saved_cpu_idle_disable_state[cpu][state] = disabled;
> +	}
> +
> +	return nr_states;
> +}
> +
> +/*
> + * restore_cpu_idle_disable_state - restore disable for all idle states of a cpu
> + *
> + * Restores the current disable state of all idle states of a cpu that was
> + * previously saved by save_cpu_idle_disable_state.
> + *
> + * Return: idle state count on success, negative on error
> + */
> +int restore_cpu_idle_disable_state(unsigned int cpu)
> +{
> +	unsigned int nr_states;
> +	unsigned int state;
> +	int disabled;
> +	int result;
> +

Should probably have a check to see if saved_cpu_idle_disable exists.

> +	nr_states = cpuidle_state_count(cpu);
> +
> +	if (nr_states == 0)
> +		return 0;
> +

As well as saved_cpu_idle_disable_state[cpu] exists.

Just for robustness.

> +	for (state = 0; state < nr_states; state++) {
> +		disabled = saved_cpu_idle_disable_state[cpu][state];
> +		result = cpuidle_state_disable(cpu, state, disabled);
> +		if (result < 0)
> +			return result;
> +	}
> +
> +	free(saved_cpu_idle_disable_state[cpu]);
> +	saved_cpu_idle_disable_state[cpu] = NULL;
> +	saved_cpu_idle_disable_state_alloc_ctr--;
> +	if (saved_cpu_idle_disable_state_alloc_ctr == 0) {
> +		free(saved_cpu_idle_disable_state);
> +		saved_cpu_idle_disable_state = NULL;
> +	}
> +
> +	return nr_states;
> +}
> +
> +/*
> + * free_cpu_idle_disable_states - free saved idle state disable for all cpus
> + *
> + * Frees the memory used for storing cpu idle state disable for all cpus
> + * and states.
> + *
> + * Normally, the memory is freed automatically in
> + * restore_cpu_idle_disable_state; this is mostly for cleaning up after an
> + * error.
> + */
> +void free_cpu_idle_disable_states(void)
> +{
> +	int cpu;
> +
> +	if (!saved_cpu_idle_disable_state)
> +		return;
> +
> +	for (cpu = 0; cpu < sysconf(_SC_NPROCESSORS_CONF); cpu++) {

> +		if (!saved_cpu_idle_disable_state[cpu])
> +			continue;

No need to check here. free() works fine with passing NULL to it.

-- Steve

> +		free(saved_cpu_idle_disable_state[cpu]);
> +		saved_cpu_idle_disable_state[cpu] = NULL;
> +	}
> +
> +	free(saved_cpu_idle_disable_state);
> +	saved_cpu_idle_disable_state = NULL;
> +}
> +
> +/*
> + * set_deepest_cpu_idle_state - limit idle state of cpu
> + *
> + * Disables all idle states deeper than the one given in
> + * deepest_state (assuming states with higher number are deeper).
> + *
> + * This is used to reduce the exit from idle latency. Unlike
> + * set_cpu_dma_latency, it can disable idle states per cpu.
> + *
> + * Return: idle state count on success, negative on error
> + */
> +int set_deepest_cpu_idle_state(unsigned int cpu, unsigned int deepest_state)
> +{
> +	unsigned int nr_states;
> +	unsigned int state;
> +	int result;
> +
> +	nr_states = cpuidle_state_count(cpu);
> +
> +	for (state = deepest_state + 1; state < nr_states; state++) {
> +		result = cpuidle_state_disable(cpu, state, 1);
> +		if (result < 0)
> +			return result;
> +	}
> +
> +	return nr_states;
> +}
> +#endif /* HAVE_LIBCPUPOWER_SUPPORT */
> +
>  #define _STR(x) #x
>  #define STR(x) _STR(x)
>  
> diff --git a/tools/tracing/rtla/src/utils.h b/tools/tracing/rtla/src/utils.h
> index d44513e6c66a..51b6054c2679 100644
> --- a/tools/tracing/rtla/src/utils.h
> +++ b/tools/tracing/rtla/src/utils.h
> @@ -64,6 +64,12 @@ int set_comm_sched_attr(const char *comm_prefix, struct sched_attr *attr);
>  int set_comm_cgroup(const char *comm_prefix, const char *cgroup);
>  int set_pid_cgroup(pid_t pid, const char *cgroup);
>  int set_cpu_dma_latency(int32_t latency);
> +#ifdef HAVE_LIBCPUPOWER_SUPPORT
> +int save_cpu_idle_disable_state(unsigned int cpu);
> +int restore_cpu_idle_disable_state(unsigned int cpu);
> +void free_cpu_idle_disable_states(void);
> +int set_deepest_cpu_idle_state(unsigned int cpu, unsigned int state);
> +#endif /* HAVE_LIBCPUPOWER_SUPPORT */
>  int auto_house_keeping(cpu_set_t *monitored_cpus);
>  
>  #define ns_to_usf(x) (((double)x/1000))