Re: dev_lock() question

From: John Baldwin (jhb_at_FreeBSD.org)
Date: 09/29/05

  • Next message: Robert Watson: "Re: freebsd-5.4-stable panics" 
    To: freebsd-hackers@freebsd.org, Poul-Henning Kamp <phk@FreeBSD.org>
Date: Thu, 29 Sep 2005 14:08:16 -0400

    On Thursday 29 September 2005 01:04 pm, Stanislav Sedov wrote:
    > On Thu, Sep 29, 2005 at 06:55:38PM +0200, Divacky Roman wrote:
    > > Hi,
    > >
    > > dev_lock() looks this way:
    > >
    > > void
    > > dev_lock(void)
    > > {
    > > if (!mtx_initialized(&devmtx))
    > > mtx_init(&devmtx, "cdev", NULL, MTX_DEF);
    > > mtx_lock(&devmtx);
    > > }
    > >
    > > I wonder why is the mtx_initialized checking necessary? shouldnt explicit
    > > initialization be sufficient?
    > >
    > > thnx for answer
    > >
    > > roman
    >
    > Moving "mtx_initialized()" check into mtx_init will decrease speed of other
    > mutexes initialization. We must check if it's initialized here because of
    > it's not permiited to pass already initialized mutex to mtx_init().

    Actually, you would think that it could be initialized either via an early
    SYSINIT() or in the init_mutexes() function in kern_mutex.c and thus not need
    the early check and avoid penalizing dev_lock().

    phk, how early his dev_lock needed? 

    -- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org
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  • Next message: Robert Watson: "Re: freebsd-5.4-stable panics"

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