netdev - Re: [PATCH v2 net-next 6/7] net: dsa: move dsa_switch_tree

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Message-ID: <1dcc27f7-f223-d5dd-5945-917e76b1b9df@gmail.com>
Date:   Wed, 5 Jan 2022 10:34:31 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     "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 6/7] net: dsa: move dsa_switch_tree :: ports
 and lags to first cache line

On 1/5/22 5:21 AM, Vladimir Oltean wrote:
> dst->ports is accessed most notably by dsa_master_find_slave(), which is
> invoked in the RX path.
> 
> dst->lags is accessed by dsa_lag_dev(), which is invoked in the RX path
> of tag_dsa.c.
> 
> dst->tag_ops, dst->default_proto and dst->pd don't need to be in the
> first cache line, so they are moved out by this change.
> 
> Before:
> 
> pahole -C dsa_switch_tree net/dsa/slave.o
> struct dsa_switch_tree {
>         struct list_head           list;                 /*     0    16 */
>         struct raw_notifier_head   nh;                   /*    16     8 */
>         unsigned int               index;                /*    24     4 */
>         struct kref                refcount;             /*    28     4 */
>         bool                       setup;                /*    32     1 */
> 
>         /* XXX 7 bytes hole, try to pack */
> 
>         const struct dsa_device_ops  * tag_ops;          /*    40     8 */
>         enum dsa_tag_protocol      default_proto;        /*    48     4 */
> 
>         /* XXX 4 bytes hole, try to pack */
> 
>         struct dsa_platform_data * pd;                   /*    56     8 */
>         /* --- cacheline 1 boundary (64 bytes) --- */
>         struct list_head           ports;                /*    64    16 */
>         struct list_head           rtable;               /*    80    16 */
>         struct net_device * *      lags;                 /*    96     8 */
>         unsigned int               lags_len;             /*   104     4 */
>         unsigned int               last_switch;          /*   108     4 */
> 
>         /* size: 112, cachelines: 2, members: 13 */
>         /* sum members: 101, holes: 2, sum holes: 11 */
>         /* last cacheline: 48 bytes */
> };
> 
> After:
> 
> 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 */
>         bool                       setup;                /*    56     1 */
> 
>         /* XXX 7 bytes hole, try to pack */
> 
>         /* --- cacheline 1 boundary (64 bytes) --- */
>         const struct dsa_device_ops  * tag_ops;          /*    64     8 */
>         enum dsa_tag_protocol      default_proto;        /*    72     4 */
> 
>         /* XXX 4 bytes hole, try to pack */
> 
>         struct dsa_platform_data * pd;                   /*    80     8 */
>         struct list_head           rtable;               /*    88    16 */
>         unsigned int               lags_len;             /*   104     4 */
>         unsigned int               last_switch;          /*   108     4 */
> 
>         /* size: 112, cachelines: 2, members: 13 */
>         /* sum members: 101, holes: 2, sum holes: 11 */
>         /* last cacheline: 48 bytes */
> };
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian