Re: [PATCH 00/10] drm/panthor: Reduce dma_fence signalling latency

[Boris Brezillon]

+Chia-I

On Wed, 29 Apr 2026 11:38:27 +0200
Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote:

> Right now, panthor is one of the rare drivers to signal fences
> from work items (not even from the threaded IRQ handler). We
> could move that to the threaded handler, but that would still
> leave the latency caused by the scheduling of the IRQ thread.
> 
> Instead, this patchset moves all the job IRQ processing to
> the raw IRQ handler, which is fine because what the current
> code does is demux the interrupts and deferring actual handling
> to sub work items. The only bits we keep in the IRQ path is
> the dma_fence signalling, which should be acceptable, in term
> of CPU cycles spent in the IRQ context.
> 
> Pretty much all the patches except the last two are just
> preparing the ground to get there. The second to last one
> does the thread -> IRQ transition, and the last one is some
> experimental interrupt coalescing support that I've added
> because I noticed moving job IRQ handling to the raw handler
> generates quite a lot of interrupts in some case, and having
> the system constantly interrupted like that can be
> detrimental.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> ---
> Boris Brezillon (10):
>       drm/panthor: Make panthor_irq::state a non-atomic field
>       drm/panthor: Move the register accessors before the IRQ helpers
>       drm/panthor: Replace the panthor_irq macro machinery by inline helpers
>       drm/panthor: Extend the IRQ logic to allow fast/raw IRQ handlers
>       drm/panthor: Make panthor_fw_{update,toggle}_reqs() callable from IRQ context
>       drm/panthor: Prepare the scheduler logic for FW events in IRQ context
>       drm/panthor: Automate CSG IRQ processing at group unbind time
>       drm/panthor: Automatically enable interrupts in panthor_fw_wait_acks()
>       drm/panthor: Process FW events in IRQ context
>       drm/panthor: Introduce interrupt coalescing support for job IRQs
> 
>  drivers/gpu/drm/panthor/panthor_device.h | 358 ++++++++++++++---------
>  drivers/gpu/drm/panthor/panthor_drv.c    |   1 +
>  drivers/gpu/drm/panthor/panthor_fw.c     | 226 +++++++++++++--
>  drivers/gpu/drm/panthor/panthor_fw.h     |  11 +-
>  drivers/gpu/drm/panthor/panthor_gpu.c    |  27 +-
>  drivers/gpu/drm/panthor/panthor_mmu.c    |  38 +--
>  drivers/gpu/drm/panthor/panthor_pwr.c    |  21 +-
>  drivers/gpu/drm/panthor/panthor_sched.c  | 475 ++++++++++++++-----------------
>  8 files changed, 698 insertions(+), 459 deletions(-)
> ---
> base-commit: 7455a0583a906533041a80e48c6a2e3230cce96e
> change-id: 20260429-panthor-signal-from-irq-d33684f4d292
> prerequisite-message-id: <20260427155934.416502-1-karunika.choo@xxxxxxx>
> prerequisite-patch-id: 70905a2eb09ab2b31d242a5ed5af3b42fb6a464c
> prerequisite-patch-id: aa4c22669f80328039762f25c0b3942bbadbdc89
> prerequisite-patch-id: 7f61bcee3c4bb5703900b18d5b6e0f52e622f29d
> prerequisite-patch-id: 3402f4d60aa526d40113fc3d9b3e599f8f89e705
> prerequisite-patch-id: 00ddbd3d455891f6950609614c1acd2baa78b0db
> prerequisite-patch-id: 6a9928f609e3757cadebb2df6795d0da55745f4e
> prerequisite-patch-id: fd91f68f25d4bc93eec405f0131f5ae4284bfaf2
> prerequisite-patch-id: 553958a10a0ca2f20f7883ad4c752cfc7485c5a8
> 
> Best regards,