netdev - Re: [PATCH] Compact sk_stream_mem

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Date:	Mon, 19 Nov 2007 23:22:45 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	acme@...stprotocols.net
Cc:	xemul@...nvz.org, devel@...nvz.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Compact sk_stream_mem_schedule() code

From: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Date: Mon, 19 Nov 2007 17:30:59 -0200

> Em Mon, Nov 19, 2007 at 03:13:44PM +0300, Pavel Emelyanov escreveu:
> > This function references sk->sk_prot->xxx for many times.
> > It turned out, that there's so many code in it, that gcc 
> > cannot always optimize access to sk->sk_prot's fields.
> > 
> > After saving the sk->sk_prot on the stack and comparing
> > disassembled code, it turned out that the function became
> > ~10 bytes shorter and made less dereferences (on i386 and 
> > x86_64). Stack consumption didn't grow.
> > 
> > Besides, this patch drives most of this function into the
> > 80 columns limit.
> > 
> > Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
> 
> I wonder if making it 'const struct proto *prot = sk->sk_prot;'
> 
> would make any difference.

Such experiments are always useful, but I doubt there will
be substantial gains in this case.

> Acked-by: Arnaldo Carvalho de Melo <acme@...hat.com>

I've applied the patch, thanks Pavel.
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