Re: [PATCH v4 3/4] pps: Always use ktime_get_snapshot_id() for pps_get_ts()

[Miroslav Lichvar]

On Mon, Sep 28, 2026 at 09:58:02AM +0200, Rodolfo Giometti wrote:
> On Sat, 2026-09-26 at 21:38 +0100, David Woodhouse wrote:
> > So yes, the specific code path you're looking at *does* get slightly
> > longer (50ns to the counter read instead of 30ns).
> [...]
> > However, they are *entirely* in the noise, as there's about 600 ns of
> > hardware and 2-4 *microseconds* of software latency before we even get
> > there.
> 
> Thanks for measuring it, and on real hardware with a real edge. That
> answers my concern: ~20 ns of constant cost against microseconds of
> latency upstream of the handler is not something PPS can see, and
> trading it for the removal of a non-constant error is the right
> trade.

FWIW, there are some polling versions of the pps-gpio driver (out of
tree), which provide much more stable measurements by trading
interrupts for higher CPU use and where this additional delay might be
visible.

-- 
Miroslav Lichvar