Re: [PATCH] rtla/timerlat: Lock the memory of the user-space threads

[John Ogness <john.ogness@linutronix.de>]

Hi Daniel,

On 2026-11-12, Daniel Wagner <wagi@monom.org> wrote:
> diff --git a/tools/tracing/rtla/src/timerlat_u.c b/tools/tracing/rtla/src/timerlat_u.c
> index c80edaf07b00..42aaf1d7f216 100644
> --- a/tools/tracing/rtla/src/timerlat_u.c
> +++ b/tools/tracing/rtla/src/timerlat_u.c
> @@ -69,6 +70,15 @@ static int timerlat_u_main(int cpu, struct timerlat_u_params *params)
>  		}
>  	}
>  
> +	/*
> +	 * Keep the measuring process in memory: the latency it reports
> +	 * runs until it is back in user space, and a page fault on the way
> +	 * (its code, stack or libc pages reclaimed under memory pressure)
> +	 * would count as latency. cyclictest does the same with -m.
> +	 */
> +	if (mlockall(MCL_CURRENT | MCL_FUTURE))
> +		err_msg("Could not lock timerlat u memory: %s\n", strerror(errno));
> +

Page faulting should happen _before_ the task has a real-time
priority. Real-time priorities are for real-time workloads.

Just move this up 30 lines.

John Ogness