linux-kernel - Re: [PATCH 2/7] kfifo: move out spinlock

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Message-ID: <b90c0690911170344l23d4ca11x5f3d6b04fee89aab@mail.gmail.com>
Date:	Tue, 17 Nov 2009 17:14:57 +0530
From:	Roger Quadros <quadros.roger@...il.com>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Andi Kleen <andi@...stfloor.org>,
	Amerigo Wang <xiyou.wangcong@...il.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 2/7] kfifo: move out spinlock

Hi Stefani,

 minor typo.

> diff -u -N -r kfifo1/include/linux/kfifo.h kfifo2/include/linux/kfifo.h
> --- kfifo1/include/linux/kfifo.h        2009-10-19 20:39:24.000000000 +0200
> +++ kfifo2/include/linux/kfifo.h        2009-10-19 20:58:34.000000000 +0200
> @@ -30,13 +30,12 @@
>        unsigned int size;      /* the size of the allocated buffer */
>        unsigned int in;        /* data is added at offset (in % size) */
>        unsigned int out;       /* data is extracted from off. (out % size) */
> -       spinlock_t *lock;       /* protects concurrent modifications */
>  };
>
>  extern void kfifo_init(struct kfifo *fifo, unsigned char *buffer,
> -                       unsigned int size, spinlock_t *lock);
> +                       unsigned int size);
>  extern __must_check int kfifo_alloc(struct kfifo *fifo, unsigned int size,
> -                       gfp_t gfp_mask, spinlock_t *lock);
> +                       gfp_t gfp_mask);
>  extern void kfifo_free(struct kfifo *fifo);
>  extern unsigned int __kfifo_put(struct kfifo *fifo,
>                                const unsigned char *buffer, unsigned int len);
> @@ -58,58 +57,67 @@
>  */
>  static inline void kfifo_reset(struct kfifo *fifo)
>  {
> -       unsigned long flags;
> -
> -       spin_lock_irqsave(fifo->lock, flags);
> -
>        __kfifo_reset(fifo);
> +}
> +
> +/**
> + * __kfifo_len - returns the number of bytes available in the FIFO
> + * @fifo: the fifo to be used.
> + */
> +static inline unsigned int __kfifo_len(struct kfifo *fifo)
> +{
> +       register unsigned int   out;
>
> -       spin_unlock_irqrestore(fifo->lock, flags);
> +       out = fifo->out;
> +       smp_rmb();
> +       return fifo->in - out;
>  }
>
>  /**
> - * kfifo_put - puts some data into the FIFO
> + * kfifo_put_locked - puts some data into the FIFO using a spinlock for locking
>  * @fifo: the fifo to be used.
> - * @buffer: the data to be added.
> + * @from: the data to be added.
>  * @len: the length of the data to be added.

should be @n:

> + * @lock: pointer to the spinlock to use for locking.
>  *
> - * This function copies at most @len bytes from the @buffer into
> + * This function copies at most @len bytes from the @from buffer into
>  * the FIFO depending on the free space, and returns the number of
>  * bytes copied.
>  */
> -static inline unsigned int kfifo_put(struct kfifo *fifo,
> -                               const unsigned char *buffer, unsigned int len)
> +static inline __must_check unsigned int kfifo_put_locked(struct kfifo *fifo,
> +               const unsigned char *from, unsigned int n, spinlock_t *lock)
>  {
>        unsigned long flags;
>        unsigned int ret;
>
> -       spin_lock_irqsave(fifo->lock, flags);
> +       spin_lock_irqsave(lock, flags);
>
> -       ret = __kfifo_put(fifo, buffer, len);
> +       ret = __kfifo_put(fifo, from, n);
>
> -       spin_unlock_irqrestore(fifo->lock, flags);
> +       spin_unlock_irqrestore(lock, flags);
>
>        return ret;
>  }
>
>  /**
> - * kfifo_get - gets some data from the FIFO
> + * kfifo_get_locked - gets some data from the FIFO using a spinlock for locking
>  * @fifo: the fifo to be used.
> - * @buffer: where the data must be copied.
> + * @to: where the data must be copied.
>  * @len: the size of the destination buffer.

should be @n

> + * @lock: pointer to the spinlock to use for locking.
>  *
>  * This function copies at most @len bytes from the FIFO into the
> - * @buffer and returns the number of copied bytes.
> + * @to buffer and returns the number of copied bytes.
>  */
> -static inline unsigned int kfifo_get(struct kfifo *fifo,
> -                                    unsigned char *buffer, unsigned int len)
> +static inline __must_check unsigned int kfifo_get_locked(struct kfifo *fifo,
> +       unsigned char *to, unsigned int n, spinlock_t *lock)
>  {
>        unsigned long flags;
>        unsigned int ret;
>
> -       spin_lock_irqsave(fifo->lock, flags);
> +       spin_lock_irqsave(lock, flags);
>
> -       ret = __kfifo_get(fifo, buffer, len);
> +       ret = __kfifo_get(fifo, to, n);
>
>        /*
>         * optimization: if the FIFO is empty, set the indices to 0
> @@ -118,36 +126,18 @@
>        if (fifo->in == fifo->out)
>                fifo->in = fifo->out = 0;
>
> -       spin_unlock_irqrestore(fifo->lock, flags);
> +       spin_unlock_irqrestore(lock, flags);
>
>        return ret;
>  }
--
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