linux-kernel - Re: [PATCH v3 2/4] sched: Introduce migratable()

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Message-ID: <20210817144348.kkgoytuz3766jeoz@linutronix.de>
Date:   Tue, 17 Aug 2021 16:43:48 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        rcu@...r.kernel.org, linux-rt-users@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Steven Price <steven.price@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Mike Galbraith <efault@....de>
Subject: Re: [PATCH v3 2/4] sched: Introduce migratable()

On 2021-08-11 21:13:52 [+0100], Valentin Schneider wrote:
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index debc960f41e3..8ba7b4a7ee69 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1715,6 +1715,16 @@ static inline bool is_percpu_thread(void)
>  #endif
>  }
>  
> +/* Is the current task guaranteed to stay on its current CPU? */
> +static inline bool migratable(void)
> +{
> +#ifdef CONFIG_SMP
> +	return preemptible() && !current->migration_disabled;
> +#else
> +	return true;

shouldn't this be false in the UP case?

> +#endif
> +}
> +
>  /* Per-process atomic flags. */
>  #define PFA_NO_NEW_PRIVS		0	/* May not gain new privileges. */
>  #define PFA_SPREAD_PAGE			1	/* Spread page cache over cpuset */

Sebastian