On Tue, 12 May 2026 14:04:43 -0700 Chia-I Wu <[email protected]> wrote:
> On Tue, May 12, 2026 at 5:14 AM Boris Brezillon > <[email protected]> wrote: > > > > Add a specific spinlock for events processing, and force processing > > of events in the panthor_sched_report_fw_events() path rather than > > deferring it to a work item. We also fast-track fence signalling by > > making the job completion logic IRQ-safe. > > > > Note that it requires changing a couple spin_lock() into > > spin_lock_irqsave() when those are taken inside a events_lock section. > > > > Signed-off-by: Boris Brezillon <[email protected]> > > --- > > drivers/gpu/drm/panthor/panthor_sched.c | 332 > > +++++++++++++++----------------- > > 1 file changed, 155 insertions(+), 177 deletions(-) > > > > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c > > b/drivers/gpu/drm/panthor/panthor_sched.c > > index 5b34032deff8..fbf76b59b7ef 100644 > > --- a/drivers/gpu/drm/panthor/panthor_sched.c > > +++ b/drivers/gpu/drm/panthor/panthor_sched.c > > @@ -177,18 +177,6 @@ struct panthor_scheduler { > > */ > > struct work_struct sync_upd_work; > > > > - /** > > - * @fw_events_work: Work used to process FW events outside the > > interrupt path. > > - * > > - * Even if the interrupt is threaded, we need any event processing > > - * that require taking the panthor_scheduler::lock to be processed > > - * outside the interrupt path so we don't block the tick logic when > > - * it calls panthor_fw_{csg,wait}_wait_acks(). Since most of the > > - * event processing requires taking this lock, we just delegate all > > - * FW event processing to the scheduler workqueue. > > - */ > > - struct work_struct fw_events_work; > > - > > /** > > * @fw_events: Bitmask encoding pending FW events. > > */ > If we process all fw events in the irq context, we can remove > fw_events as well. More on this below. Oops, forgot to remove this field, indeed. > > @@ -254,6 +242,15 @@ struct panthor_scheduler { > > struct list_head waiting; > > } groups; > > > > + /** > > + * @events_lock: Lock taken when processing events. > > + * > > + * This also needs to be taken when csg_slots are updated, to make > > sure > > + * the event processing logic doesn't touch groups that have left > > the CSG > > + * slot. > > + */ > > + spinlock_t events_lock; > > + > > /** > > * @csg_slots: FW command stream group slots. > It looks like read access can use either lock (process context) or > events_lock (irq context), while write access must use events_lock > (process context). Can we put that into the comment, or if makes > sense, enforce that with accessor functions? You're right. I'll mention that updates to csg_slots[] must be done with both the ::lock and ::events_lock held, while reads can be done with any of them held. > > > > */ > > @@ -676,9 +673,6 @@ struct panthor_group { > > */ > > struct panthor_kernel_bo *protm_suspend_buf; > > > > - /** @sync_upd_work: Work used to check/signal job fences. */ > > - struct work_struct sync_upd_work; > > - > Can we make this a preparatory commit, where group_sync_upd_work is > replaced by group_check_job_completion? I'll try to split that up. > > Multiple things happen in this commit. I try to identify things that > can be separate commits. If this does not make sense, feel free to > ignore. > > > /** @tiler_oom_work: Work used to process tiler OOM events > > happening on this group. */ > > struct work_struct tiler_oom_work; > > [...] > > /** > > * panthor_sched_report_fw_events() - Report FW events to the scheduler. > > * @ptdev: Device. > > @@ -1902,8 +1953,19 @@ void panthor_sched_report_fw_events(struct > > panthor_device *ptdev, u32 events) > This can be renamed to panthor_sched_handle_fw_events. It's not quite handling events though. For most of them, it's really just deferring the processing to work items, SYNC_UPDATE is the exception. > > > if (!ptdev->scheduler) > > return; > > > > - atomic_or(events, &ptdev->scheduler->fw_events); > > - sched_queue_work(ptdev->scheduler, fw_events); > > + guard(spinlock_irqsave)(&ptdev->scheduler->events_lock); > > + > > + if (events & JOB_INT_GLOBAL_IF) { > > + sched_process_global_irq_locked(ptdev); > > + events &= ~JOB_INT_GLOBAL_IF; > > + } > > + > > + while (events) { > > + u32 csg_id = ffs(events) - 1; > > + > > + sched_process_csg_irq_locked(ptdev, csg_id); > > + events &= ~BIT(csg_id); > > + } > This handles all fw events in the irq context. Are there concerns that > it may take too long? I might be wrong, but it seems possible to > handle only CSG_SYNC_UPDATE and defer the rest as before. I started with just the SYNC_UPDATE processing done in the hard-irq context, but after auditing the other stuff done in the handler, I realized it's basically just deferring all actual processing to work items. Yes, there's the overhead of demuxing the events from the ack/req regs, but part of this is already done to get to SYNC_UPDATE anyway, so at this point we're probably better off demuxing everything and scheduling works for all kind of events. I also compared the perfs between the two approaches (though I didn't do as much testing as I did with the new version, so I might have missed something), and it didn't seem to matter at all, because the interrupts we receive the most are SYNC_UPDATE and IDLE events, and those are at the same level.
