linux-kernel - Re: [PATCH 1/6] x86: drop unneded members of struct cpuinfo

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Message-ID: <20170214161700.fmrp2a4hl2fsjevs@pd.tnic>
Date:   Tue, 14 Feb 2017 17:17:00 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Mathias Krause <minipli@...glemail.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jesper Nilsson <jesper.nilsson@...s.com>,
        Mikael Starvik <starvik@...s.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 1/6] x86: drop unneded members of struct cpuinfo_x86

On Sun, Feb 12, 2017 at 10:12:07PM +0100, Mathias Krause wrote:
> Those member serve no purpose -- not even fill padding for alignment or
> such. So just get rid of them.

Well, almost. You need the wp_works_ok removal patch too, otherwise you
have the 3 bytes hole below.

But the wp_works_ok goes away too so I guess that's fine.

$ pahole -C cpuinfo_x86 vmlinux
struct cpuinfo_x86 {
        __u8                       x86;                  /*     0     1 */
        __u8                       x86_vendor;           /*     1     1 */
        __u8                       x86_model;            /*     2     1 */
        __u8                       x86_mask;             /*     3     1 */
        char                       wp_works_ok;          /*     4     1 */
        __u8                       x86_virt_bits;        /*     5     1 */
        __u8                       x86_phys_bits;        /*     6     1 */
        __u8                       x86_coreid_bits;      /*     7     1 */
        __u8                       cu_id;                /*     8     1 */

        /* XXX 3 bytes hole, try to pack */

        __u32                      extended_cpuid_level; /*    12     4 */
        int                        cpuid_level;          /*    16     4 */
        __u32                      x86_capability[19];   /*    20    76 */
        /* --- cacheline 1 boundary (64 bytes) was 32 bytes ago --- */
        char                       x86_vendor_id[16];    /*    96    16 */
        char                       x86_model_id[64];     /*   112    64 */
        /* --- cacheline 2 boundary (128 bytes) was 48 bytes ago --- */
        int                        x86_cache_size;       /*   176     4 */
        int                        x86_cache_alignment;  /*   180     4 */
        int                        x86_cache_max_rmid;   /*   184     4 */
        int                        x86_cache_occ_scale;  /*   188     4 */
        /* --- cacheline 3 boundary (192 bytes) --- */
        int                        x86_power;            /*   192     4 */
        long unsigned int          loops_per_jiffy;      /*   196     4 */
        u16                        x86_max_cores;        /*   200     2 */
        u16                        apicid;               /*   202     2 */
        u16                        initial_apicid;       /*   204     2 */
        u16                        x86_clflush_size;     /*   206     2 */
        u16                        booted_cores;         /*   208     2 */
        u16                        phys_proc_id;         /*   210     2 */
        u16                        logical_proc_id;      /*   212     2 */
        u16                        cpu_core_id;          /*   214     2 */
        u16                        cpu_index;            /*   216     2 */

        /* XXX 2 bytes hole, try to pack */

        u32                        microcode;            /*   220     4 */

        /* size: 224, cachelines: 4, members: 30 */
        /* sum members: 219, holes: 2, sum holes: 5 */
        /* last cacheline: 32 bytes */
};

-- 
Regards/Gruss,
    Boris.

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