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Message-ID: <3A42B353.D0D249C1@innominate.de>
Date: Fri, 22 Dec 2000 02:50:11 +0100
From: Daniel Phillips <phillips@innominate.de>
Organization: innominate
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To: Paul Cassella <pwc@sgi.com>, Tim Wright <timw@splhi.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC] Semaphores used for daemon wakeup
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Paul Cassella wrote:
> The sync variable version of the dmabuf code snippet (assuming the
> dmabuf_mutex is never acquired from an interrupt) would look like this:
> 
>     dmabuf_init(...);
>     {
>             ...
>             spin_lock_init(&dmabuf_spin);
>             sv_init(&dmabuf_sv, &dmabuf_spin, SV_MON_SPIN);
>             ...
>     }
> 
>     dmabuf_alloc(...)
>     {
> 
>             ...
>             while (1) {
>                     spin_lock(&dmabuf_spin);
>                     attempt to grab a free buffer;
>                     if (success){
>                             spin_unlock(&dmabuf_spin);
>                             return;
>                     } else {
>                             sv_wait(&dmabuf_sv);
>                     }
>             }
>     }
> 
>     dmabuf_free(...)
>     {
>             ...
>             spin_lock(&dmabuf_spin);
>             free up buffer;
>             sv_broadcast(&dmabuf_sv);
>             spin_unlock(&dmabuf_spin);
>     }
> 

But isn't this actually a simple situation?  How about:

    dmabuf_alloc(...)
    {
            ...
            while (1) {
                    spin_lock(&dmabuf_lock);
                    attempt to grab a free buffer;
                    spin_unlock(&dmabuf_lock);
                    if (success)
                           return;
                    down(&dmabuf_wait);
            }
    }

    dmabuf_free(...)
    {
            ...
            spin_lock(&dmabuf_lock);
            free up buffer;
            spin_unlock(&dmabuf_lock);
            up(&dmabuf_wait);
    }

--
Daniel
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