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From: John Baldwin <jhb@FreeBSD.org>
To: freebsd-hackers@freebsd.org,
 Poul-Henning Kamp <phk@FreeBSD.org>
Date: Thu, 29 Sep 2005 14:08:16 -0400
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Cc: Divacky Roman <xdivac02@stud.fit.vutbr.cz>, Stanislav Sedov <stas@310.ru>
Subject: Re: dev_lock() question
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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