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From: Leonardo Bras <leobras@redhat.com>
To: Kent Overstreet <kent.overstreet@linux.dev>
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Subject: Re: [PATCH 16/50] sched.h: Move (spin|rwlock)_needbreak() to spinlock.h
Date: Mon, 15 Jan 2024 17:31:34 -0300
Message-ID: <ZaWWJsq2j-TjKxJI@LeoBras>
In-Reply-To: <20231216032651.3553101-6-kent.overstreet@linux.dev>
References: <20231216024834.3510073-1-kent.overstreet@linux.dev> <20231216032651.3553101-1-kent.overstreet@linux.dev> <20231216032651.3553101-6-kent.overstreet@linux.dev>
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On Fri, Dec 15, 2023 at 10:26:15PM -0500, Kent Overstreet wrote:
> This lets us kill the dependency on spinlock.h.
> 
> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
> ---
>  include/linux/sched.h    | 31 -------------------------------
>  include/linux/spinlock.h | 31 +++++++++++++++++++++++++++++++
>  2 files changed, 31 insertions(+), 31 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 5a5b7b122682..7501a3451a20 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2227,37 +2227,6 @@ static inline bool preempt_model_preemptible(void)
>  	return preempt_model_full() || preempt_model_rt();
>  }
>  
> -/*
> - * Does a critical section need to be broken due to another
> - * task waiting?: (technically does not depend on CONFIG_PREEMPTION,
> - * but a general need for low latency)
> - */
> -static inline int spin_needbreak(spinlock_t *lock)
> -{
> -#ifdef CONFIG_PREEMPTION
> -	return spin_is_contended(lock);
> -#else
> -	return 0;
> -#endif
> -}
> -
> -/*
> - * Check if a rwlock is contended.
> - * Returns non-zero if there is another task waiting on the rwlock.
> - * Returns zero if the lock is not contended or the system / underlying
> - * rwlock implementation does not support contention detection.
> - * Technically does not depend on CONFIG_PREEMPTION, but a general need
> - * for low latency.
> - */
> -static inline int rwlock_needbreak(rwlock_t *lock)
> -{
> -#ifdef CONFIG_PREEMPTION
> -	return rwlock_is_contended(lock);
> -#else
> -	return 0;
> -#endif
> -}
> -
>  static __always_inline bool need_resched(void)
>  {
>  	return unlikely(tif_need_resched());
> diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
> index 31d3d747a9db..0c71f06454d9 100644
> --- a/include/linux/spinlock.h
> +++ b/include/linux/spinlock.h
> @@ -449,6 +449,37 @@ static __always_inline int spin_is_contended(spinlock_t *lock)
>  	return raw_spin_is_contended(&lock->rlock);
>  }
>  
> +/*
> + * Does a critical section need to be broken due to another
> + * task waiting?: (technically does not depend on CONFIG_PREEMPTION,
> + * but a general need for low latency)
> + */
> +static inline int spin_needbreak(spinlock_t *lock)
> +{
> +#ifdef CONFIG_PREEMPTION
> +	return spin_is_contended(lock);
> +#else
> +	return 0;
> +#endif
> +}
> +
> +/*
> + * Check if a rwlock is contended.
> + * Returns non-zero if there is another task waiting on the rwlock.
> + * Returns zero if the lock is not contended or the system / underlying
> + * rwlock implementation does not support contention detection.
> + * Technically does not depend on CONFIG_PREEMPTION, but a general need
> + * for low latency.
> + */
> +static inline int rwlock_needbreak(rwlock_t *lock)
> +{
> +#ifdef CONFIG_PREEMPTION
> +	return rwlock_is_contended(lock);
> +#else
> +	return 0;
> +#endif
> +}
> +
>  #define assert_spin_locked(lock)	assert_raw_spin_locked(&(lock)->rlock)
>  
>  #else  /* !CONFIG_PREEMPT_RT */
> -- 
> 2.43.0


Hello Kent,

This patch is breaking PREEMPT_RT builds, but it can be easily fixed.

I sent a patch on the fix, please take a look:
https://lore.kernel.org/all/20240115201935.2326400-1-leobras@redhat.com/

Thanks!
Leo