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From: Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua>
To: Paul Jackson <pj@sgi.com>
Subject: Re: [Patch 17/23] mask v2 = [6/7] nodemask_t_ia64_changes
Date: Wed, 7 Apr 2004 08:55:03 +0300
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On Tuesday 06 April 2004 14:37, Paul Jackson wrote:
> Matthew,
>
> A couple of these nodemask changes are increasing kernel text size quite
> a bit on big numa configurations.
>
> I've got one test case I ran where the text size of vmlinux increased
> from 8789097 to 8810513 bytes (2.6.5 kernel for ia64 SN2 NR_CPUS=512
> sn2_defconfig, gcc 3.2.3).
>
> From a cursory comparson of 'nm --print-size --size-sort' output,
> I think the increased space is caused by the numerous numnodes
> changes, such as:
>
> -			pxm_to_nid_map[i] = numnodes;
> -			nid_to_pxm_map[numnodes++] = i;
> +			pxm_to_nid_map[i] = num_online_nodes();
> +			nid_to_pxm_map[num_online_nodes()] = i;
> +			node_set_online(num_online_nodes());
>
> And by the for loop replacements:
>
> -	for (nid = 0, i = 0; i < numnodes; i++)  {
> +	nid = 0;
> +	for_each_online_node(i) {
>
> In particular, the machine code generated by the following silly little
> routine:
>
>  int foo() { int i = 0, n; for_each_online_node(n) i++; return i; }
>
> is ... hold onto your hat ...
>
> a000000100116f40 <foo>:
> a000000100116f40:	00 10 20 02 29 26 	[MII]       addl r2=-2091896,r1
> a000000100116f46:	80 00 00 00 42 20 	            mov r8=r0
> a000000100116f4c:	02 00 08 90       	            mov r17=256

<~700 bytes of code snipped away>

> a000000100117256:	00 00 00 02 00 80 	            nop.i 0x0
> a00000010011725c:	08 00 84 00       	            br.ret.sptk.many b0;;

Deinlining will help, but why such a simple thing require 700 bytes of code in
the first place? (assuming it's not a gcc drain bamage and non-inlined
for_each_online_node(n) will be of comparable size)
-- 
vda
-
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