Date: Mon, 24 Jan 2005 18:49:25 -0800
From: Andrew Morton <akpm@osdl.org>
To: george@mvista.com
Cc: roland@redhat.com, torvalds@osdl.org, linux-kernel@vger.kernel.org,
       clameter@sgi.com, drepper@redhat.com
Subject: Re: [PATCH 1/7] posix-timers: tidy up clock interfaces and
 consolidate dispatch logic
Message-Id: <20050124184925.19a1ea75.akpm@osdl.org>
In-Reply-To: <41F5ABB8.8070308@mvista.com>
References: <200501232322.j0NNMcxe006476@magilla.sf.frob.com>
	<41F5ABB8.8070308@mvista.com>
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George Anzinger <george@mvista.com> wrote:
>
>  >  /*
>   > + * Define this to initialize every k_clock function table so all its
>   > + * function pointers are non-null, and always do indirect calls through the
>   > + * table.  Leave it undefined to instead leave null function pointers and
>   > + * decide at the call sites between a direct call (maybe inlined) to the
>   > + * default function and an indirect call through the table when it's filled
>   > + * in.  Which style is preferable is whichever performs better in the
>   > + * common case of using the default functions.
> 
>   > +#define CLOCK_DISPATCH_DIRECT
> 
>  As I understand it modern machines, the indirect call does really bad things to 
>  the pipeline.  The default call, even preceeded by the if, will be much faster 
>  by this reasoning.  I would, therefor, prefer not defining CLOCK_DISPATCH_DIRECT.

We do need to do one or the other.  I assume the current indecision is
pending some benchmarking work?
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