linux-kernel - Re: [PATCH rcu 3/7] locking: Reduce the number of locks in ww

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Message-ID: <2e8a6800-78e7-42bf-b4ff-5d7ef43511c5@paulmck-laptop>
Date:   Fri, 17 Mar 2023 11:38:19 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     rcu@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Shuah Khan <shuah@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        seanjc@...gle.com, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH rcu 3/7] locking: Reduce the number of locks in ww_mutex
 stress tests

On Thu, Mar 16, 2023 at 08:13:35PM -0700, Boqun Feng wrote:
> The stress test in test_ww_mutex_init() uses 4095 locks since
> lockdep::reference has 12 bits, and since we are going to reduce it to
> 11 bits to support lock_sync(), and 2047 is still a reasonable number of
> the max nesting level for locks, so adjust the test.
> 
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Link: https://lore.kernel.org/oe-lkp/202302011445.9d99dae2-oliver.sang@intel.com
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>

Tested-by: Paul E. McKenney <paulmck@...nel.org>

> ---
>  kernel/locking/test-ww_mutex.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
> index 29dc253d03af..93cca6e69860 100644
> --- a/kernel/locking/test-ww_mutex.c
> +++ b/kernel/locking/test-ww_mutex.c
> @@ -659,7 +659,7 @@ static int __init test_ww_mutex_init(void)
>  	if (ret)
>  		return ret;
>  
> -	ret = stress(4095, hweight32(STRESS_ALL)*ncpus, STRESS_ALL);
> +	ret = stress(2047, hweight32(STRESS_ALL)*ncpus, STRESS_ALL);
>  	if (ret)
>  		return ret;
>  
> -- 
> 2.39.2
>