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Date: Thu, 19 Mar 2015 23:10:21 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: mingo@kernel.org, rusty@rustcorp.com.au, mathieu.desnoyers@efficios.com,
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Subject: Re: [PATCH 6/8] rbtree: Implement generic latch_tree
Message-ID: <20150319221021.GT2896@worktop.programming.kicks-ass.net>
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On Thu, Mar 19, 2015 at 01:58:33PM -0700, Andrew Morton wrote:
> On Thu, 19 Mar 2015 08:25:02 +0100 Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Wed, Mar 18, 2015 at 10:14:46PM -0700, Andrew Morton wrote:
> > > On Wed, 18 Mar 2015 14:36:32 +0100 Peter Zijlstra <peterz@infradead.org> wrote:
> > > 
> > > >  include/linux/rbtree_latch.h |  223 +++++++++++++++++++++++++++++++++++++++++++
> > > 
> > > Did it really need to all be inlined?
> > 
> > Without that you get actual function calls to the less() and comp()
> > operators. This way GCC can inline the lot even though its function
> > pointers.
> > 
> > The typical RB tree user open-codes all this every single time.
> 
> Is it a good tradeoff?

Is what? Writing it like this or open-coding it all?

For many archs (indirect) function calls are far more expensive than the
typical comparison.