Re: [RFC][PATCH 1/3] drm: drm_syncobj: Add note in DOC about absolute timeout values

[Christian König]

Am 12.07.22 um 06:22 schrieb John Stultz:
> After having to debug down through the kernel to figure out
> why my _WAIT calls were always timing out, I realized its
> an absolute timeout value instead of the more common relative
> timeouts.
>
> This detail should be called out in the documentation, as while
> the absolute value makes sense here, its not as common for timeout
> values.

Well absolute timeout values are mandatory for making -ERESTARTSYS work 
without any additional handling.

So using them is recommended for ~20 years now and IIRC even documented 
somewhere.

See here as well https://lwn.net/Articles/17744/ how much trouble system 
calls with relative timeouts are.

Regards,
Christian.

> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Maxime Ripard <mripard@xxxxxxxxxx>
> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Cc: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
> Cc: Chunming Zhou <david1.zhou@xxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
> ---
>   drivers/gpu/drm/drm_syncobj.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 7e48dcd1bee4..b84d842a1c21 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -136,6 +136,10 @@
>    * requirement is inherited from the wait-before-signal behavior required by
>    * the Vulkan timeline semaphore API.
>    *
> + * It should be noted, that both &DRM_IOCTL_SYNCOBJ_WAIT and
> + * &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT takes an *absolute* CLOCK_MONOTONIC
> + * nanosecond value for the timeout value. Accidentally passing relative time
> + * values will likely result in an immediate -ETIME return.
>    *
>    * Import/export of syncobjs
>    * -------------------------