| Message ID | 20250305130551.136682-3-phasta@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | drm/sched: Documentation and refcount improvements | expand |
On Wed, Mar 05, 2025 at 02:05:50PM +0100, Philipp Stanner wrote: > /** > - * @run_job: Called to execute the job once all of the dependencies > - * have been resolved. This may be called multiple times, if > - * timedout_job() has happened and drm_sched_job_recovery() > - * decides to try it again. > + * @run_job: Called to execute the job once all of the dependencies > + * have been resolved. > + * > + * @sched_job: the job to run > + * > + * The deprecated drm_sched_resubmit_jobs() (called by &struct > + * drm_sched_backend_ops.timedout_job) can invoke this again with the > + * same parameters. Using this is discouraged because it violates > + * dma_fence rules, notably dma_fence_init() has to be called on > + * already initialized fences for a second time. Moreover, this is > + * dangerous because attempts to allocate memory might deadlock with > + * memory management code waiting for the reset to complete. > + * > + * TODO: Document what drivers should do / use instead. No replacement? Or bespoke/roll-your-own functionality as a must? Confused...
On Wed, 2025-03-05 at 20:45 +0700, Bagas Sanjaya wrote: > On Wed, Mar 05, 2025 at 02:05:50PM +0100, Philipp Stanner wrote: > > /** > > - * @run_job: Called to execute the job once all of the > > dependencies > > - * have been resolved. This may be called multiple times, > > if > > - * timedout_job() has happened and > > drm_sched_job_recovery() > > - * decides to try it again. > > + * @run_job: Called to execute the job once all of the > > dependencies > > + * have been resolved. > > + * > > + * @sched_job: the job to run > > + * > > + * The deprecated drm_sched_resubmit_jobs() (called by > > &struct > > + * drm_sched_backend_ops.timedout_job) can invoke this > > again with the > > + * same parameters. Using this is discouraged because it > > violates > > + * dma_fence rules, notably dma_fence_init() has to be > > called on > > + * already initialized fences for a second time. Moreover, > > this is > > + * dangerous because attempts to allocate memory might > > deadlock with > > + * memory management code waiting for the reset to > > complete. > > + * > > + * TODO: Document what drivers should do / use instead. > > No replacement? Or bespoke/roll-your-own functionality as a must? > > Confused... We will document this in a follow-up. I'm trying for 2 months now [1] just to fix up some broken, outdated documentation – and that in a component that *I* am maintaining. It's very difficult to reach the relevant stakeholders, and I really want to unblock this series. Feel free to provide a proposal for the TODO based on this series or jump into the discussion here [2]. Otherwise I will propose a fix for the TODO some time the next weeks. P. [1] https://lore.kernel.org/dri-devel/20250109133710.39404-2-phasta@kernel.org/ [2] https://lore.kernel.org/dri-devel/688b5665-496d-470d-9835-0c6eadfa5569@gmail.com/
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h index 50928a7ae98e..6381baae8024 100644 --- a/include/drm/gpu_scheduler.h +++ b/include/drm/gpu_scheduler.h @@ -410,10 +410,36 @@ struct drm_sched_backend_ops { struct drm_sched_entity *s_entity); /** - * @run_job: Called to execute the job once all of the dependencies - * have been resolved. This may be called multiple times, if - * timedout_job() has happened and drm_sched_job_recovery() - * decides to try it again. + * @run_job: Called to execute the job once all of the dependencies + * have been resolved. + * + * @sched_job: the job to run + * + * The deprecated drm_sched_resubmit_jobs() (called by &struct + * drm_sched_backend_ops.timedout_job) can invoke this again with the + * same parameters. Using this is discouraged because it violates + * dma_fence rules, notably dma_fence_init() has to be called on + * already initialized fences for a second time. Moreover, this is + * dangerous because attempts to allocate memory might deadlock with + * memory management code waiting for the reset to complete. + * + * TODO: Document what drivers should do / use instead. + * + * This method is called in a workqueue context - either from the + * submit_wq the driver passed through drm_sched_init(), or, if the + * driver passed NULL, a separate, ordered workqueue the scheduler + * allocated. + * + * Note that the scheduler expects to 'inherit' its own reference to + * this fence from the callback. It does not invoke an extra + * dma_fence_get() on it. Consequently, this callback must take a + * reference for the scheduler, and additional ones for the driver's + * respective needs. + * + * Return: + * * On success: dma_fence the driver must signal once the hardware has + * completed the job ("hardware fence"). + * * On failure: NULL or an ERR_PTR. */ struct dma_fence *(*run_job)(struct drm_sched_job *sched_job);
The documentation for drm_sched_backend_ops.run_job() mentions a certain function called drm_sched_job_recovery(). This function does not exist. What's actually meant is drm_sched_resubmit_jobs(), which is by now also deprecated. Furthermore, the scheduler expects to "inherit" a reference on the fence from the run_job() callback. This, so far, is also not documented. Remove the mention of the removed function. Discourage the behavior of drm_sched_backend_ops.run_job() being called multiple times for the same job. Document the necessity of incrementing the refcount in run_job(). Signed-off-by: Philipp Stanner <phasta@kernel.org> --- include/drm/gpu_scheduler.h | 34 ++++++++++++++++++++++++++++++---- 1 file changed, 30 insertions(+), 4 deletions(-)