netdev - Re: [PATCH v2 net-next 0/7] Cleanup to main DSA structures

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Message-ID: <20220105185901.hprorcjw6api4bwc@skbuf>
Date:   Wed, 5 Jan 2022 18:59:01 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>
Subject: Re: [PATCH v2 net-next 0/7] Cleanup to main DSA structures

On Wed, Jan 05, 2022 at 10:39:04AM -0800, Florian Fainelli wrote:
> On 1/5/22 5:21 AM, Vladimir Oltean wrote:
> > This series contains changes that do the following:
> >
> > - struct dsa_port reduced from 576 to 544 bytes, and first cache line a
> >   bit better organized
> > - struct dsa_switch from 160 to 136 bytes, and first cache line a bit
> >   better organized
> > - struct dsa_switch_tree from 112 to 104 bytes, and first cache line a
> >   bit better organized
> >
> > No changes compared to v1, just split into a separate patch set.
>
> This is all looking good to me. I suppose we could possibly swap the
> 'nh' and 'tag_ops' member since dst->tag_ops is used in
> dsa_tag_generic_flow_dissect() which is a fast path, what do you think?

pahole is telling me that dst->tag_ops is in the first cache line on
both arm64 and arm32. Are you saying that it's better for it to take
dst->nh's place?

[/opt/arm64-linux] $ pahole -C dsa_switch_tree net/dsa/slave.o
struct dsa_switch_tree {
        struct list_head           list;                 /*     0    16 */
        struct list_head           ports;                /*    16    16 */
        struct raw_notifier_head   nh;                   /*    32     8 */
        unsigned int               index;                /*    40     4 */
        struct kref                refcount;             /*    44     4 */
        struct net_device * *      lags;                 /*    48     8 */
        const struct dsa_device_ops  * tag_ops;          /*    56     8 */
        /* --- cacheline 1 boundary (64 bytes) --- */
        enum dsa_tag_protocol      default_proto;        /*    64     4 */
        bool                       setup;                /*    68     1 */

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

        struct dsa_platform_data * pd;                   /*    72     8 */
        struct list_head           rtable;               /*    80    16 */
        unsigned int               lags_len;             /*    96     4 */
        unsigned int               last_switch;          /*   100     4 */

        /* size: 104, cachelines: 2, members: 13 */
        /* sum members: 101, holes: 1, sum holes: 3 */
        /* last cacheline: 40 bytes */
};

[/opt/arm-linux] $ pahole -C dsa_switch_tree net/dsa/slave.o
struct dsa_switch_tree {
        struct list_head           list;                 /*     0     8 */
        struct list_head           ports;                /*     8     8 */
        struct raw_notifier_head   nh;                   /*    16     4 */
        unsigned int               index;                /*    20     4 */
        struct kref                refcount;             /*    24     4 */
        struct net_device * *      lags;                 /*    28     4 */
        const struct dsa_device_ops  * tag_ops;          /*    32     4 */
        enum dsa_tag_protocol      default_proto;        /*    36     4 */
        bool                       setup;                /*    40     1 */

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

        struct dsa_platform_data * pd;                   /*    44     4 */
        struct list_head           rtable;               /*    48     8 */
        unsigned int               lags_len;             /*    56     4 */
        unsigned int               last_switch;          /*    60     4 */

        /* size: 64, cachelines: 1, members: 13 */
        /* sum members: 61, holes: 1, sum holes: 3 */
};