linux-kernel - Re: [PATCH v5 3/3] rseq/selftests: Add test for mm

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Message-ID: <da68dc94-9aa8-4ee1-b0f9-e28eb5c7da56@efficios.com>
Date: Mon, 10 Feb 2025 15:53:12 +0100
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Gabriele Monaco <gmonaco@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, "Paul E. McKenney"
 <paulmck@...nel.org>, Shuah Khan <shuah@...nel.org>,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v5 3/3] rseq/selftests: Add test for mm_cid compaction

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@...icios.com>

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

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