Re: [PATCH v2] tracing/osnoise: Add option to align tlat threads

[Wander Lairson Costa <wander@redhat.com>]

On Mon, Mar 02, 2026 at 02:13:16PM +0100, Tomas Glozar wrote:
> Add an option called TIMERLAT_ALIGN to osnoise/options, together with a
> corresponding setting osnoise/timerlat_align_us.
> 
> This option sets the alignment of wakeup times between different
> timerlat threads, similarly to cyclictest's -A/--aligned option. If
> TIMERLAT_ALIGN is set, the first thread that reaches the first cycle
> records its first wake-up time. Each following thread sets its first
> wake-up time to a fixed offset from the recorded time, and increments
> it by the same offset.
> 
> Example:
> 
> osnoise/timerlat_period is set to 1000, osnoise/timerlat_align_us is
> set to 20. There are four threads, on CPUs 1 to 4.
> 
> - CPU 4 enters first cycle first. The current time is 20000us, so
> the wake-up of the first cycle is set to 21000us. This time is recorded.
> - CPU 2 enter first cycle next. It reads the recorded time, increments
> it to 21020us, and uses this value as its own wake-up time for the first
> cycle.
> - CPU 3 enters first cycle next. It reads the recorded time, increments
> it to 21040 us, and uses the value as its own wake-up time.
> - CPU 1 proceeds analogically.
> 
> In each next cycle, the wake-up time (called "absolute period" in
> timerlat code) is incremented by the (relative) period of 1000us. Thus,
> the wake-ups in the following cycles (provided the times are reached and
> not in the past) will be as follows:
> 
> CPU 1		CPU 2		CPU 3	 	CPU 4
> 21080us		21020us		21040us		21000us
> 22080us		22020us		22040us		22000us
> ...		...		...		...
> 

Reviewed-by: Wander Lairson Costa <wander@redhat.com>