On 6/28/20 2:27 AM, Dmitry Osipenko wrote:
23.06.2020 15:09, Mikko Perttunen пишет:### IOCTL HOST1X_ALLOCATE_SYNCPOINT (on /dev/host1x) Allocates a free syncpoint, returning a file descriptor representing it. Only the owner of the file descriptor is allowed to mutate the value of the syncpoint. ``` struct host1x_ctrl_allocate_syncpoint { /** * @fd: * * [out] New file descriptor representing the allocated syncpoint. */ __s32 fd; __u32 reserved[3]; };We should need at least these basic things from the sync points API > - Execution context shouldn't be able to tamper sync points of the other contexts.
This is covered by this UAPI - when submitting, as part of the syncpt_incr struct you pass the syncpoint FD. This way the driver can check the syncpoints used are correct, or program HW protection.
- Sync point could be shared with other contexts for explicit fencing.
Not sure what you specifically mean; you can get the ID out of the syncpoint fd and share the ID for read-only access. (Or the FD for read-write access)
- Sync points should work reliably. Some problems of the current Host1x driver, like where it falls over if sync point value is out-of-sync + all the hang-job recovery labor could be easily reduced if sync point health is protected by extra UAPI constraints. > So I think we may want the following: 1. We still should need to assign sync point ID to a DRM-channel's context. This sync point ID will be used for a commands stream forming, like it is done by the current staging UAPI. So we should need to retain the DRM_TEGRA_GET_SYNCPT IOCTL, but improve it. 2. Allocated sync point must have a clean hardware state.
What do you mean by clean hardware state?
3. Sync points should be properly refcounted. Job's sync points shouldn't be re-used while job is alive. 4. The job's sync point can't be re-used after job's submission (UAPI constraint!). Userspace must free sync point and allocate a new one for the next job submission. And now we: - Know that job's sync point is always in a healthy state! - We're not limited by a number of physically available hardware sync points! Allocation should block until free sync point is available. - The logical number of job's sync point increments matches the SP hardware state! Which is handy for a job's debugging. Optionally, the job's sync point could be auto-removed from the DRM's context after job's submission, avoiding a need for an extra SYNCPT_PUT IOCTL invocation to be done by userspace after the job's submission. Could be a job's flag.
I think this would cause problems where after a job completes but before the fence has been waited, the syncpoint is already recycled (especially if the syncpoint is reset into some clean state).
I would prefer having a syncpoint for each userspace channel context (several of which could share a hardware channel if MLOCKing is not used).
In my experience it's then not difficult to pinpoint which job has failed, and if each userspace channel context uses a separate syncpoint, a hanging job wouldn't mess with other application's jobs, either.
Mikko
We could avoid a need for a statically-allocated sync points at all for a patched cmdstreams! The sync point could be dynamically allocated at a job's submission time by the kernel driver and then cmdstream will be patched with this sync point.
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