[Mesa-dev] [PATCH 4/5] i965: perf: add support for userspace configurations

[Chris Wilson]

Quoting Lionel Landwerlin (2017-08-29 11:58:57)
> This allows us to deploy new configurations without touching the
> kernel.
> 
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> ---
>  src/mesa/drivers/dri/i965/brw_performance_query.c | 97 ++++++++++++++++++++++-
>  1 file changed, 96 insertions(+), 1 deletion(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_performance_query.c b/src/mesa/drivers/dri/i965/brw_performance_query.c
> index 4b585c95b7d..901cbb464e9 100644
> --- a/src/mesa/drivers/dri/i965/brw_performance_query.c
> +++ b/src/mesa/drivers/dri/i965/brw_performance_query.c
> @@ -1807,6 +1807,96 @@ read_sysfs_drm_device_file_uint64(struct brw_context *brw,
>     return read_file_uint64(buf, value);
>  }
>  
> +static bool
> +kernel_has_dynamic_config_support(int drm_fd, const char *sysfs_dev_dir)
> +{
> +    struct drm_i915_perf_oa_config config;
> +    const char *uuid = "01234567-0123-0123-0123-0123456789ab";
> +    uint32_t mux_regs[] = { 0x9888 /* NOA_WRITE */, 0x0 };
> +    char config_path[256];
> +    struct stat sb;
> +    uint64_t config_id;
> +    int ret;
> +
> +    snprintf(config_path, sizeof(config_path),
> +             "%s/metrics/%s/id", sysfs_dev_dir, uuid);
> +
> +    if (stat(config_path, &sb) == 0) {
> +       if (!read_file_uint64(config_path, &config_id))
> +          return false;
> +
> +       if (ioctl(drm_fd, DRM_IOCTL_I915_PERF_REMOVE_CONFIG, &config_id) == 0)
> +          return true;

So you acknowledge the race condition with another process also doing
the same test, or worse if they genuinely used that uuid for an actual
config.

> +    }
> +
> +    memset(&config, 0, sizeof(config));
> +    memcpy(config.uuid, uuid, sizeof(config.uuid));
> +
> +    config.n_mux_regs = 1;
> +    config.mux_regs_ptr = (uintptr_t) mux_regs;
> +
> +    /* Create a new config */
> +    ret = ioctl(drm_fd, DRM_IOCTL_I915_PERF_ADD_CONFIG, &config);
> +    if (ret < 0)
> +        return false;

A trick you may like to try is to create an invalid config that
generates something other than EINVAL so that you can then distinguish
with the non-existent ioctl cmd error. Since you reserved id=0 for
invalid, a good choice would be

static bool has_dyn_config() {
	uint64_t config_id = 0;
	return sys_ioctl(drm_fd, DRM_IOCTL_I915_PERF_REMOVE_CONFIG, &config_id) == -ENOENT;
}
-Chris