Re: [PATCH v5 0/3] pps: improve PREEMPT_RT performance

[Calvin Owens]

On Saturday 05/16 at 13:32 +0200, Michael Byczkowski wrote:
> > On 25. Apr 2026, at 19:18, Michael Byczkowski <by@xxxxxxxxxxxx> wrote:
> >
> > I found three issues in the PPS subsystem that cause unnecessary jitter
> > under PREEMPT_RT, while being fully backward-compatible with non-RT
> > kernels:
> > 
> > 1. pps-gpio: The IRQ handler is force-threaded on PREEMPT_RT, so the
> > PPS timestamp is captured after scheduling delay rather than at
> > interrupt entry. Fix: split into a hardirq primary handler (captures
> > timestamp only) and a threaded handler (processes the event).
> > 
> > 2. pps_device.lock: spinlock_t becomes a sleeping mutex on PREEMPT_RT,
> > allowing pps_event() to be preempted mid-update. Fix: convert to
> > raw_spinlock_t and move sleeping calls out of the critical section.
> > 
> > 3. pps_kc_hardpps_lock: Same issue as (2), in the kernel consumer path
> > that calls hardpps(). Fix: convert to DEFINE_RAW_SPINLOCK.
> > 
> > All three patches are tested on a Raspberry Pi 5 running a 7.0.0-rc6
> > PREEMPT_RT kernel. On non-RT kernels there is zero behavioral change.
> > 
> > Signed-off-by: Michael Byczkowski <by@xxxxxxxxxxxx>
> > Acked-by: Rodolfo Giometti <giometti@xxxxxxxxxxxx>
> > Tested-by: Michael Byczkowski <by@xxxxxxxxxxxx>
> > 
> > by (3):
> > pps: pps-gpio: split IRQ handler into hardirq and threaded parts
> > pps: convert pps_device lock to raw_spinlock for PREEMPT_RT
> > pps: convert pps_kc_hardpps_lock to raw_spinlock for PREEMPT_RT
> > 
> > drivers/pps/clients/pps-gpio.c | 37 +++++++++++++++++++++++-----------
> > drivers/pps/kapi.c             | 18 ++++++++++-------
> > drivers/pps/kc.c               | 22 ++++++++++----------
> > drivers/pps/pps.c              | 16 +++++++--------
> > include/linux/pps_kernel.h     |  2 +-
> > 5 files changed, 56 insertions(+), 39 deletions(-)
> > 
> > -- 
> > 2.47.3
>
> Gentle ping on this series. v4 patches 1/3 and 3/3 carried Rodolfo's
> Acked-by; v5 addressed the remaining feedback on 2/3. Happy to rework
> anything or split the series if that helps it move forward.

Unfortunately apple mail is corrupting your patches :/

Greg KH usually applies patches for drivers/pps/, but I didn't add him
here yet because the patches don't apply.

If you can point me at a git branch for v5, I'd be happy to re-send the
patches myself with your authorship. This is all useful for me and I'd
like to help :)

If you do it yourself, just make sure to add Greg to the Cc: list.

Cheers,
Calvin

> Adding linux-rt-users@ and Sebastian on Cc in case there's interest from the
> PREEMPT_RT side.