[PATCH v3 1/2] lib: Add DRM driver sysfs profiling knob toggling functions

[Zbigniew Kempczyński]

On Fri, May 10, 2024 at 08:15:20PM +0100, Adrián Larumbe wrote:
> Some DRM drivers need to have their accounting HW toggled on demand from
> user space so that fdinfo's drm-engine and drm-cycles tags can be updated
> upon job completion.
> 
> A profiler such as gputop should be able to check which DRM devices have
> such a sysfs knob, record its original state, toggle-enable it and revert
> this operation right before exiting.
> 
> Also create a new static library dependency for this family of functions so
> that it can later be linked against gputop.
> 
> Cc: Tvrtko Ursulin <tursulin at ursulin.net>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> Cc: Kamil Konieczny <kamil.konieczny at linux.intel.com>
> Cc: Lucas De Marchi <lucas.demarchi at intel.com>
> Signed-off-by: Adrián Larumbe <adrian.larumbe at collabora.com>
> ---
>  lib/igt_profiling.c | 141 ++++++++++++++++++++++++++++++++++++++++++++
>  lib/igt_profiling.h |  21 +++++++
>  lib/meson.build     |   8 +++
>  3 files changed, 170 insertions(+)
>  create mode 100644 lib/igt_profiling.c
>  create mode 100644 lib/igt_profiling.h
> 
> diff --git a/lib/igt_profiling.c b/lib/igt_profiling.c
> new file mode 100644
> index 000000000000..f5ac40d072ac
> --- /dev/null
> +++ b/lib/igt_profiling.c
> @@ -0,0 +1,141 @@
> +// SPDX-License-Identifier: MIT
> +/*
> + * Copyright © 2024 Collabora Ltd.
> + * Copyright © 2024 Adrian Larumbe <adrian.larumbe at collabora.com>
> + * Copyright © 2024 Amazon.com, Inc. or its affiliates.
> + *
> + */
> +
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <dirent.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <assert.h>
> +#include <stdbool.h>
> +
> +#include "igt_profiling.h"
> +
> +#define SYSFS_DRM	"/sys/class/drm"
> +#define NUM_DEVICES	10
> +
> +struct igt_profiled_device *igt_devices_profiled(void)
> +{
> +	struct igt_profiled_device *profiled_devices;
> +	unsigned int devlist_len = NUM_DEVICES;
> +	unsigned int i = 0;
> +	struct dirent *entry;
> +	DIR *dev_dir;
> +
> +	/* The return array will be resized in case there are too many devices */
> +	profiled_devices = malloc(devlist_len * sizeof(struct igt_profiled_device));
> +	if (!profiled_devices)
> +		return NULL;
> +
> +	dev_dir = opendir(SYSFS_DRM);
> +	if (!dev_dir) {

		goto end;

> +		free(profiled_devices);
> +		return NULL;
> +	}
> +
> +	while ((entry = readdir(dev_dir)) != NULL) {
> +		char path[PATH_MAX];
> +		char orig_state;
> +		int sysfs_fd;
> +
> +		/* All DRM device entries are symlinks to other paths within sysfs */
> +		if (entry->d_type != DT_LNK)
> +			continue;
> +
> +		/* We're only interested in render nodes */
> +		if (strstr(entry->d_name, "render") != entry->d_name)
> +			continue;
> +
> +		snprintf(path, sizeof(path), "%s/%s/device/%s",
> +			 SYSFS_DRM, entry->d_name, "profiling");
> +
> +		if (access(path, F_OK))
> +			continue;
> +
> +		sysfs_fd = open(path, O_RDONLY);
> +		if (sysfs_fd == -1)
> +			continue;
> +
> +		if (read(sysfs_fd, &orig_state, 1) <= 0) {
> +			close(sysfs_fd);
> +			continue;
> +		}
> +
> +		if (i == (devlist_len - 1)) {
> +			devlist_len += NUM_DEVICES;
> +			profiled_devices = realloc(profiled_devices, devlist_len);
> +		}
> +
> +		profiled_devices[i].syspath = strdup(path);

According to realloc above - if it will fail we'll get segfault here.

> +		profiled_devices[i++].original_state = orig_state;
> +
> +		close(sysfs_fd);
> +	}
> +

end:

> +	if (i == 0) {
> +		free(profiled_devices);
> +		profiled_devices = NULL;
> +	} else
> +		profiled_devices[i].syspath = NULL; /* Array terminator */
> +
> +	return profiled_devices;
> +}
> +
> +
> +void igt_devices_toggle_profiling(struct igt_profiled_device *devices, bool enable)

I think you should document this. Function sets profiling if enable == 1,
for enable == 0 it restores original state. For me 'toggle' is a little
bit confusing - I would rather expect 0 -> 1 and 1 -> 0 state change but
you're restoring original state. Maybe 'set_profiling' would be better?

> +{
> +	assert(devices);
> +
> +	for (unsigned int i = 0; devices[i].syspath; i++) {
> +
> +		int sysfs_fd = open(devices[i].syspath, O_WRONLY);
> +
> +		if (sysfs_fd < 0)
> +			continue;
> +
> +		write(sysfs_fd, enable ? "1" : &devices[i].original_state, 1);
> +		close(sysfs_fd);
> +	}
> +}
> +
> +void igt_devices_free_profiling(struct igt_profiled_device *devices)
> +{
> +	assert(devices);
> +
> +	for (unsigned int i = 0; devices[i].syspath; i++)
> +		free(devices[i].syspath);
> +
> +	free(devices);
> +}
> +
> +void igt_devices_update_original_profiling_state(struct igt_profiled_device *devices)

You may use igt_devices_toggle_profiling(devices, true); to achieve
the same effect (adding read() which checks on which devices profiling
is still set to 0). I assume igt_devices_profiled() collects original
state which should be restored so it's state should be const.

> +{
> +	assert(devices);
> +
> +	for (unsigned int i = 0; devices[i].syspath; i++) {
> +		char new_state;
> +		int sysfs_fd;
> +
> +		sysfs_fd = open(devices[i].syspath, O_RDWR);
> +		if (sysfs_fd == -1)
> +			continue;
> +
> +		if (!read(sysfs_fd, &new_state, 1)) {
> +			close(sysfs_fd);
> +			continue;
> +		}

Only reason I see new_state could be changed if external process
would change it. Otherwise it is same to state from igt_devices_profiled().

--
Zbigniew

> +
> +		if (new_state == '0') {
> +			write(sysfs_fd, "1", 1);
> +			devices[i].original_state = new_state;
> +		}
> +
> +		close(sysfs_fd);
> +	}
> +}
> diff --git a/lib/igt_profiling.h b/lib/igt_profiling.h
> new file mode 100644
> index 000000000000..fd0835d9a699
> --- /dev/null
> +++ b/lib/igt_profiling.h
> @@ -0,0 +1,21 @@
> +/* SPDX-License-Identifier: MIT */
> +/*
> + * Copyright © 2024 Collabora Ltd.
> + * Copyright © 2024 Adrian Larumbe <adrian.larumbe at collabora.com>
> + * Copyright © 2024 Amazon.com, Inc. or its affiliates.
> + */
> +
> +#ifndef IGT_PROFILING_H
> +#define IGT_PROFILING_H
> +
> +struct igt_profiled_device {
> +	char *syspath;
> +	char original_state;
> +};
> +
> +void igt_devices_toggle_profiling(struct igt_profiled_device *devices, bool enable);
> +struct igt_profiled_device *igt_devices_profiled(void);
> +void igt_devices_free_profiling(struct igt_profiled_device *devices);
> +void igt_devices_update_original_profiling_state(struct igt_profiled_device *devices);
> +
> +#endif /* IGT_PROFILING_H */
> diff --git a/lib/meson.build b/lib/meson.build
> index e2f740c116f8..6f61ed5c558b 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -291,6 +291,14 @@ lib_igt_drm_fdinfo_build = static_library('igt_drm_fdinfo',
>  
>  lib_igt_drm_fdinfo = declare_dependency(link_with : lib_igt_drm_fdinfo_build,
>  				  include_directories : inc)
> +
> +lib_igt_profiling_build = static_library('igt_profiling',
> +	['igt_profiling.c'],
> +	include_directories : inc)
> +
> +lib_igt_profiling = declare_dependency(link_with : lib_igt_profiling_build,
> +				        include_directories : inc)
> +
>  i915_perf_files = [
>    'igt_list.c',
>    'i915/perf.c',
> -- 
> 2.44.0
>