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Message-ID: <20190417135659.GH4038@hirez.programming.kicks-ass.net>
Date: Wed, 17 Apr 2019 15:56:59 +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>,
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 v4 11/16] locking/rwsem: Enable readers spinning on writer
On Sat, Apr 13, 2019 at 01:22:54PM -0400, Waiman Long wrote:
> @@ -549,7 +582,7 @@ static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem)
> return !owner ? OWNER_NULL : OWNER_READER;
> }
>
> -static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
> +static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock)
> {
> bool taken = false;
> bool is_rt_task = rt_task(current);
> @@ -558,9 +591,6 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
> preempt_disable();
>
> /* sem->wait_lock should not be held when doing optimistic spinning */
> - if (!rwsem_can_spin_on_owner(sem))
> - goto done;
> -
> if (!osq_lock(&sem->osq))
> goto done;
>
> @@ -580,10 +610,11 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
> /*
> * Try to acquire the lock
> */
> - if (rwsem_try_write_lock_unqueued(sem)) {
> - taken = true;
> + taken = wlock ? rwsem_try_write_lock_unqueued(sem)
> + : rwsem_try_read_lock_unqueued(sem);
> +
> + if (taken)
> break;
> - }
>
> /*
> * An RT task cannot do optimistic spinning if it cannot
Alternatively you pass the trylock function as an argument:
static bool rwsem_optimistic_spin(struct rw_semaphore *sem,
bool (*trylock)(struct rw_semaphore *sem))
{
...
if (trylock(sem)) {
taken = true;
goto unlock;
}
...
}
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