On Tue, 19 May 2026 10:16:26 -0700 Chia-I Wu <[email protected]> wrote:
> On Tue, May 19, 2026 at 12:53 AM Boris Brezillon > <[email protected]> wrote: > > > > On Mon, 18 May 2026 16:33:20 -0700 > > Chia-I Wu <[email protected]> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 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. > > > > > Looking at ftrace irq events, when there is one active csg, > > > > > panthor-job takes 6us (median) / 17us (95%) / 27us (slowest). > > > > > > > > > > I don't have a good sense if that's considered normal in hardirq. But > > > > > if that is ever an issue, and if the majority of the time is spent in > > > > > CSG_SYNC_UPDATE anyway, we can always revert the last patch to move > > > > > processing to threaded handler. > > > > > > > > Actually, the threaded -> hard transition (patch 9) is where the perf > > > > gain is. > > > hardirq is even more timely for sure. For our use case, the threaded > > > handler is RT and is also good enough. > > > > Yeah, true. I forgot you were forcing RT priority on threaded handlers. > > Anyway, let's stick to hardirqs for now, and revisit it if it proves to > > be too much work done in irq context. > Just want to clarify that irq_thread calls sched_set_fifo to make the > task RT. The behavior is universal and is not specific to any > downstream kernel. Hm, interesting. In my testing, any of the changes before patch 9 didn't make a huge difference in term of perf, patch 9 is where the perf gains happen. For the record, patch 6 is where we get rid of the threaded -> work round-trip for job completion/fence signaling, and it didn't seem to reflect in the benchmark results, but I'll do another round of tests before posting v3, just to confirm.
