netdev - Re: [PATCH] mlx5: work around high stack usage with gcc

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Message-Id: <20200106.133448.1654261172205332113.davem@redhat.com>
Date:   Mon, 06 Jan 2020 13:34:48 -0800 (PST)
From:   David Miller <davem@...hat.com>
To:     arnd@...db.de
Cc:     saeedm@...lanox.com, leon@...nel.org,
        adhemerval.zanella@...aro.org, tariqt@...lanox.com,
        shayag@...lanox.com, eranbe@...lanox.com, maximmi@...lanox.com,
        ayal@...lanox.com, moshe@...lanox.com, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mlx5: work around high stack usage with gcc

From: Arnd Bergmann <arnd@...db.de>
Date: Sat,  4 Jan 2020 22:51:44 +0100

> In some configurations, gcc tries too hard to optimize this code:
> 
> drivers/net/ethernet/mellanox/mlx5/core/en_stats.c: In function 'mlx5e_grp_sw_update_stats':
> drivers/net/ethernet/mellanox/mlx5/core/en_stats.c:302:1: error: the frame size of 1336 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> 
> As was stated in the bug report, the reason is that gcc runs into a corner
> case in the register allocator that is rather hard to fix in a good way.
> 
> As there is an easy way to work around it, just add a comment and the
> barrier that stops gcc from trying to overoptimize the function.
> 
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92657
> Cc: Adhemerval Zanella <adhemerval.zanella@...aro.org>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Saeed, please take this.

Thank you.