Subject: Re: [PATCH] Priority Lists for the RT mutex
From: Steven Rostedt <rostedt@goodmis.org>
To: dwalker@mvista.com
Cc: linux-kernel@vger.kernel.org,
       "Perez-Gonzalez, Inaky" <inaky.perez-gonzalez@intel.com>,
       Oleg Nesterov <oleg@tv-sign.ru>, Ingo Molnar <mingo@elte.hu>
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Organization: Kihon Technologies
Date: Mon, 09 May 2005 15:21:46 -0400
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On Mon, 2005-05-09 at 11:13 -0700, Daniel Walker wrote:
> On Mon, 2005-05-09 at 02:11, Ingo Molnar wrote:
> 
> > What would be nice to achieve are [low-cost] reductions of the size of 
> > struct rt_mutex (in include/linux/rt_lock.h), upon which all other 
> > PI-aware locking objects are based. Right now it's 9 words, of which 
> > struct plist is 5 words. Would be nice to trim this to 8 words - which 
> > would give a nice round size of 32 bytes on 32-bit.
> 
> Why not make rt_mutex->wait_lock a pointer ? Set it to NULL and handle
> it in rt.c .

That may make the rt_mutex structure smaller but this increases the size
of the kernel by the size of that pointer (times every rt_mutex in the
kernel!). You still need to allocate the size of the raw spin lock,
although now you just point to it. Is rounding worth that much overhead?

-- Steve

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