linux-kernel - Re: [PATCH v3 2/5] locking/qspinlock: Refactor the qspinlock slow path

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Message-ID: <20190716102034.GN3419@hirez.programming.kicks-ass.net>
Date:   Tue, 16 Jul 2019 12:20:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alex Kogan <alex.kogan@...cle.com>
Cc:     linux@...linux.org.uk, mingo@...hat.com, will.deacon@....com,
        arnd@...db.de, longman@...hat.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        guohanjun@...wei.com, jglauber@...vell.com,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        dave.dice@...cle.com, rahul.x.yadav@...cle.com
Subject: Re: [PATCH v3 2/5] locking/qspinlock: Refactor the qspinlock slow
 path

On Mon, Jul 15, 2019 at 03:25:33PM -0400, Alex Kogan wrote:

> +/*
> + * set_locked_empty_mcs - Try to set the spinlock value to _Q_LOCKED_VAL,
> + * and by doing that unlock the MCS lock when its waiting queue is empty
> + * @lock: Pointer to queued spinlock structure
> + * @val: Current value of the lock
> + * @node: Pointer to the MCS node of the lock holder
> + *
> + * *,*,* -> 0,0,1
> + */
> +static __always_inline bool __set_locked_empty_mcs(struct qspinlock *lock,
> +						   u32 val,
> +						   struct mcs_spinlock *node)
> +{
> +	return atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL);
> +}

That name is nonsense. It should be something like:

static __always_inline bool __try_clear_tail(...)


> +/*
> + * pass_mcs_lock - pass the MCS lock to the next waiter
> + * @node: Pointer to the MCS node of the lock holder
> + * @next: Pointer to the MCS node of the first waiter in the MCS queue
> + */
> +static __always_inline void __pass_mcs_lock(struct mcs_spinlock *node,
> +					    struct mcs_spinlock *next)
> +{
> +	arch_mcs_spin_unlock_contended(&next->locked, 1);
> +}

I'm not entirely happy with that name either; but it's not horrible like
the other one. Why not mcs_spin_unlock_contended() ?