Re: [PATCHv4 net-next 09/10] net: add gso_ipv4_max_size and gro_ipv4_max_size per device

[Xin Long <lucien.xin@gmail.com>]

On Tue, Jan 31, 2023 at 9:59 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Sat, 2023-01-28 at 10:58 -0500, Xin Long wrote:
> > This patch introduces gso_ipv4_max_size and gro_ipv4_max_size
> > per device and adds netlink attributes for them, so that IPV4
> > BIG TCP can be guarded by a separate tunable in the next patch.
> >
> > To not break the old application using "gso/gro_max_size" for
> > IPv4 GSO packets, this patch updates "gso/gro_ipv4_max_size"
> > in netif_set_gso/gro_max_size() if the new size isn't greater
> > than GSO_LEGACY_MAX_SIZE, so that nothing will change even if
> > userspace doesn't realize the new netlink attributes.
>
> Not a big deal, but I think it would be nice to include the pahole info
> showing where the new fields are located and why that are good
> locations.
>
> No need to send a new version for just for the above, unless Eric asks
> otherwise ;)
>
The the pahole info without and with the patch shows below:

- Without the Patch:

# pahole --hex -C net_device vmlinux
struct net_device {
...
long unsigned int          gro_flush_timeout;    /* 0x330   0x8 */
int                        napi_defer_hard_irqs; /* 0x338   0x4 */
unsigned int               gro_max_size;         /* 0x33c   0x4 */  <---------
/* --- cacheline 13 boundary (832 bytes) --- */
rx_handler_func_t *        rx_handler;           /* 0x340   0x8 */
void *                     rx_handler_data;      /* 0x348   0x8 */
struct mini_Qdisc *        miniq_ingress;        /* 0x350   0x8 */
struct netdev_queue *      ingress_queue;        /* 0x358   0x8 */
struct nf_hook_entries *   nf_hooks_ingress;     /* 0x360   0x8 */
unsigned char              broadcast[32];        /* 0x368  0x20 */
/* --- cacheline 14 boundary (896 bytes) was 8 bytes ago --- */
struct cpu_rmap *          rx_cpu_rmap;          /* 0x388   0x8 */
struct hlist_node          index_hlist;          /* 0x390  0x10 */

/* XXX 32 bytes hole, try to pack */

/* --- cacheline 15 boundary (960 bytes) --- */
struct netdev_queue *      _tx __attribute__((__aligned__(64))); /*
0x3c0   0x8 */
...

/* --- cacheline 32 boundary (2048 bytes) was 24 bytes ago --- */
const struct attribute_group  * sysfs_groups[4]; /* 0x818  0x20 */
const struct attribute_group  * sysfs_rx_queue_group; /* 0x838   0x8 */
/* --- cacheline 33 boundary (2112 bytes) --- */
const struct rtnl_link_ops  * rtnl_link_ops;     /* 0x840   0x8 */
unsigned int               gso_max_size;         /* 0x848   0x4 */
unsigned int               tso_max_size;         /* 0x84c   0x4 */
u16                        gso_max_segs;         /* 0x850   0x2 */
u16                        tso_max_segs;         /* 0x852   0x2 */   <---------

/* XXX 4 bytes hole, try to pack */

const struct dcbnl_rtnl_ops  * dcbnl_ops;        /* 0x858   0x8 */
s16                        num_tc;               /* 0x860   0x2 */
struct netdev_tc_txq       tc_to_txq[16];        /* 0x862  0x40 */
/* --- cacheline 34 boundary (2176 bytes) was 34 bytes ago --- */
u8                         prio_tc_map[16];      /* 0x8a2  0x10 */
...
}


- With the Patch:

For "gso_ipv4_max_size", it filled the hole as expected.

/* --- cacheline 33 boundary (2112 bytes) --- */
const struct rtnl_link_ops  * rtnl_link_ops;     /* 0x840   0x8 */
unsigned int               gso_max_size;         /* 0x848   0x4 */
unsigned int               tso_max_size;         /* 0x84c   0x4 */
u16                        gso_max_segs;         /* 0x850   0x2 */
u16                        tso_max_segs;         /* 0x852   0x2 */
unsigned int               gso_ipv4_max_size;    /* 0x854   0x4 */ <-------
const struct dcbnl_rtnl_ops  * dcbnl_ops;        /* 0x858   0x8 */
s16                        num_tc;               /* 0x860   0x2 */
struct netdev_tc_txq       tc_to_txq[16];        /* 0x862  0x40 */
/* --- cacheline 34 boundary (2176 bytes) was 34 bytes ago --- */
u8                         prio_tc_map[16];      /* 0x8a2  0x10 */


For "gro_ipv4_max_size", these are no byte holes, I just put it
in the "Cache lines mostly used on receive path" area, and
next to gro_max_size.

long unsigned int          gro_flush_timeout;    /* 0x330   0x8 */
int                        napi_defer_hard_irqs; /* 0x338   0x4 */
unsigned int               gro_max_size;         /* 0x33c   0x4 */
/* --- cacheline 13 boundary (832 bytes) --- */
unsigned int               gro_ipv4_max_size;    /* 0x340   0x4 */  <------

/* XXX 4 bytes hole, try to pack */

rx_handler_func_t *        rx_handler;           /* 0x348   0x8 */
void *                     rx_handler_data;      /* 0x350   0x8 */
struct mini_Qdisc *        miniq_ingress;        /* 0x358   0x8 */
struct netdev_queue *      ingress_queue;        /* 0x360   0x8 */
struct nf_hook_entries *   nf_hooks_ingress;     /* 0x368   0x8 */
unsigned char              broadcast[32];        /* 0x370  0x20 */
/* --- cacheline 14 boundary (896 bytes) was 16 bytes ago --- */
struct cpu_rmap *          rx_cpu_rmap;          /* 0x390   0x8 */
struct hlist_node          index_hlist;          /* 0x398  0x10 */

/* XXX 24 bytes hole, try to pack */

/* --- cacheline 15 boundary (960 bytes) --- */
struct netdev_queue *      _tx __attribute__((__aligned__(64))); /*
0x3c0   0x8 */


Thanks.