Subject: Re: __attribute__((always_inline)) fiasco
From: Albert Cahalan <albert@users.sf.net>
To: Richard Henderson <rth@twiddle.net>
Cc: Albert Cahalan <albert@users.sourceforge.net>,
       linux-kernel mailing list <linux-kernel@vger.kernel.org>
In-Reply-To: <20040923165406.GB11968@twiddle.net>
References: <1095956778.4966.940.camel@cube>
	 <20040923165406.GB11968@twiddle.net>
Content-Type: text/plain
Organization: 
Message-Id: <1095961600.4973.958.camel@cube>
Mime-Version: 1.0
Date: 23 Sep 2004 13:46:40 -0400
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1124
Lines: 34

On Thu, 2004-09-23 at 12:54, Richard Henderson wrote:
> On Thu, Sep 23, 2004 at 12:26:18PM -0400, Albert Cahalan wrote:
> > Are benchmarks significantly affected if you remove the inline?
> 
> The routines in question expand to exactly one instruction.

Fine, but that's not what I asked.

I asked if it shows up on benchmarks. It doesn't, does it?

Supposing that it does, then you might use the
alternate instruction replacement trick for this.
That will beat function pointers for speed.

Also, a simple conditional branch might be better
predicted than a function pointer anyway. At least
it will be close.

So you have at least four reasonable choices:

a. don't inline at all
b. have an uninline_foo() version for each foo
c. instruction replacement
d. simple conditional

The simple choices are better, unless you have
benchmarks (whole system ones) that show otherwise.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/