Re: [PATCH v5 3/3] rseq/selftests: Add test for mm_cid compaction

[Mathieu Desnoyers]

On 2025-02-10 08:57, Gabriele Monaco wrote:
> A task in the kernel (task_mm_cid_work) runs somewhat periodically to
> compact the mm_cid for each process. Add a test to validate that it runs
> correctly and timely.
>
> The test spawns 1 thread pinned to each CPU, then each thread, including
> the main one, runs in short bursts for some time. During this period, the
> mm_cids should be spanning all numbers between 0 and nproc.
>
> At the end of this phase, a thread with high enough mm_cid (>= nproc/2)
> is selected to be the new leader, all other threads terminate.
>
> After some time, the only running thread should see 0 as mm_cid, if that
> doesn't happen, the compaction mechanism didn't work and the test fails.
>
> The test never fails if only 1 core is available, in which case, we
> cannot test anything as the only available mm_cid is 0.
>
> To: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

tiny nit below:

> +		usleep(RUNNER_PERIOD);
> +	curr_mm_cid = rseq_current_mm_cid();
> +	/*
> +	 * We select one thread with high enough mm_cid to be the new leader

Missing punctuation here (...new leader.  All other...)

> +	 * all other threads (including the main thread) will terminate.
> +	 * After some time, the mm_cid of the only remaining thread should
> +	 * converge to 0, if not, the test fails.
> +	 */

Thanks,

Mathieu


--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com