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Message-ID: <0877d757-275e-2c82-0e08-5c9ccd27be1c@intel.com>
Date:   Fri, 17 Feb 2023 14:28:05 +0100
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Muhammad Sammar <muhammads@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
CC:     kernel test robot <lkp@...el.com>, <llvm@...ts.linux.dev>,
        <oe-kbuild-all@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re:
 drivers/net/ethernet/mellanox/mlx5/core/steering/dr_ste_v0.c:1170:1: warning:
 stack frame size (1168) exceeds limit (1024) in
 'dr_ste_v0_build_eth_ipv6_l3_l4_tag'

From: Kernel Test Robot <lkp@...el.com>
Date: Fri, 17 Feb 2023 13:26:53 +0800

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   3ac88fa4605ec98e545fb3ad0154f575fda2de5f
> commit: 7766c9b922febe18b4eb124eb731dd9a1ec71373 net/mlx5: DR, Add missing reserved fields to dr_match_param
> date:   1 year, 2 months ago
> config: powerpc-allyesconfig (https://download.01.org/0day-ci/archive/20230217/202302171359.vvB4yivq-lkp@intel.com/config)
> compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project db89896bbbd2251fff457699635acbbedeead27f)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install powerpc cross compiling tool for clang build
>         # apt-get install binutils-powerpc-linux-gnu
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7766c9b922febe18b4eb124eb731dd9a1ec71373
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 7766c9b922febe18b4eb124eb731dd9a1ec71373
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash drivers/net/ethernet/mellanox/ drivers/platform/ drivers/staging/
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@...el.com>
> | Link: https://lore.kernel.org/oe-kbuild-all/202302171359.vvB4yivq-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>>> drivers/net/ethernet/mellanox/mlx5/core/steering/dr_ste_v0.c:1170:1: warning: stack frame size (1168) exceeds limit (1024) in 'dr_ste_v0_build_eth_ipv6_l3_l4_tag' [-Wframe-larger-than]
>    dr_ste_v0_build_eth_ipv6_l3_l4_tag(struct mlx5dr_match_param *value,
>    ^
>    56/1168 (4.79%) spills, 1112/1168 (95.21%) variables

I wondered a bit regarding this warning, please see below.

>    1 warning generated.
> 
> 
> vim +/dr_ste_v0_build_eth_ipv6_l3_l4_tag +1170 drivers/net/ethernet/mellanox/mlx5/core/steering/dr_ste_v0.c
> 
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1168  
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1169  static int
> d65e841de80375 Yevgeny Kliteynik 2020-11-19 @1170  dr_ste_v0_build_eth_ipv6_l3_l4_tag(struct mlx5dr_match_param *value,
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1171  				   struct mlx5dr_ste_build *sb,
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1172  				   u8 *tag)
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1173  {
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1174  	struct mlx5dr_match_spec *spec = sb->inner ? &value->inner : &value->outer;
> 0733535d59e154 Yevgeny Kliteynik 2021-07-04  1175  	struct mlx5dr_match_misc *misc = &value->misc;
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1176  
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1177  	DR_STE_SET_TAG(eth_l4, tag, dst_port, spec, tcp_dport);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1178  	DR_STE_SET_TAG(eth_l4, tag, src_port, spec, tcp_sport);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1179  	DR_STE_SET_TAG(eth_l4, tag, dst_port, spec, udp_dport);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1180  	DR_STE_SET_TAG(eth_l4, tag, src_port, spec, udp_sport);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1181  	DR_STE_SET_TAG(eth_l4, tag, protocol, spec, ip_protocol);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1182  	DR_STE_SET_TAG(eth_l4, tag, fragmented, spec, frag);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1183  	DR_STE_SET_TAG(eth_l4, tag, dscp, spec, ip_dscp);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1184  	DR_STE_SET_TAG(eth_l4, tag, ecn, spec, ip_ecn);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1185  	DR_STE_SET_TAG(eth_l4, tag, ipv6_hop_limit, spec, ttl_hoplimit);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1186  
> 0733535d59e154 Yevgeny Kliteynik 2021-07-04  1187  	if (sb->inner)
> 0733535d59e154 Yevgeny Kliteynik 2021-07-04  1188  		DR_STE_SET_TAG(eth_l4, tag, flow_label, misc, inner_ipv6_flow_label);
> 0733535d59e154 Yevgeny Kliteynik 2021-07-04  1189  	else
> 0733535d59e154 Yevgeny Kliteynik 2021-07-04  1190  		DR_STE_SET_TAG(eth_l4, tag, flow_label, misc, outer_ipv6_flow_label);
> 0733535d59e154 Yevgeny Kliteynik 2021-07-04  1191  
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1192  	if (spec->tcp_flags) {
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1193  		DR_STE_SET_TCP_FLAGS(eth_l4, tag, spec);
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1194  		spec->tcp_flags = 0;
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1195  	}

So you have 11 _SET_TAG() here (each of them is MLX5_SET()) + one
_SET_TCP_FLAGS(), which in fact is 9 more MLX5_SET(). Total 20 and
MLX5_SET() hides a u32 inside. 20 * 4 = 80 bytes, so I still doesn't
fully understand how it becomes 1112 bytes. Probably each _SET() expands
to something more than just one integer (it has a lot of calculations
inside, however, all of them are compile-time constants, so dunno).

One proposal would be to move this block:

	if (tcp_flags) {
		SET_TCP_FLAGS();
		tcp_flags = 0;
	}

into a separate noinline function. Or to try to optimize MLX5_SET()
somehow :D

> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1196  
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1197  	return 0;
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1198  }
> d65e841de80375 Yevgeny Kliteynik 2020-11-19  1199  
> 
> :::::: The code at line 1170 was first introduced by commit
> :::::: d65e841de80375372f9842ed71756d3b90d96dc4 net/mlx5: DR, Move HW STEv0 match logic to a separate file
> 
> :::::: TO: Yevgeny Kliteynik <kliteyn@...dia.com>
> :::::: CC: Saeed Mahameed <saeedm@...dia.com>
> 

Thanks,
Olek

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