linux-kernel - Re: [PATCH v8 15/19] locking/rwsem: Adaptive disabling of reader optimistic spinning

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Message-ID: <20190604092008.GJ3402@hirez.programming.kicks-ass.net>
Date:   Tue, 4 Jun 2019 11:20:08 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH v8 15/19] locking/rwsem: Adaptive disabling of reader
 optimistic spinning

On Mon, May 20, 2019 at 04:59:14PM -0400, Waiman Long wrote:
> @@ -286,6 +325,7 @@ struct rwsem_waiter {
>  	struct task_struct *task;
>  	enum rwsem_waiter_type type;
>  	unsigned long timeout;
> +	long last_rowner;
>  };
>  #define rwsem_first_waiter(sem) \
>  	list_first_entry(&sem->wait_list, struct rwsem_waiter, list)

> +static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
> +					      long last_rowner)

> +static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
> +					      unsigned long last_rowner)

> +	waiter.last_rowner = atomic_long_read(&sem->owner);

That's somewhat inconsistent wrt the type. I'll make it unsigned long,
as that is what makes most sense, given there's a pointer inside.