[ovs-dev] [PATCH 09/12] dpif: Reorder elements in dpif_upcall structure.

[Bodireddy, Bhanuprakash]

Hello jarno,

Thanks for the feedback, while reordering the members of dpif_upcall, I had to deviate from standards due to below reason.
The dp_packet member has mbuf as first member that starts at new cache line creating hole of size 60 bytes between dpif_upcall_type and dp_packet as pointed below.

struct dpif_upcall {
        enum dpif_upcall_type      type;                                                 

       -->  60 bytes hole

        /* --- cacheline 1 boundary (64 bytes) --- */
        struct dp_packet {
                struct rte_mbuf {
                        /* typedef MARKER */ void *     cacheline0[0];     /*    64     0 */

       }
       struct nlattr *            key;                                                  
.
.
}

I tried to pack this hole by moving other members in to this space. 

Regards,
Bhanu Prakash. 

>-----Original Message-----
>From: Jarno Rajahalme [mailto:jarno at ovn.org]
>Sent: Friday, October 7, 2016 10:11 PM
>To: Bodireddy, Bhanuprakash <bhanuprakash.bodireddy at intel.com>
>Cc: dev at openvswitch.org
>Subject: Re: [ovs-dev] [PATCH 09/12] dpif: Reorder elements in dpif_upcall
>structure.
>
>CodingStyle.md instructs to group struct members into related groups. Also,
>changing the relative order of pointers should not make any difference. Could
>you achieve the same by reordering just the members above the
>‘DPIF_UC_ACTION only.’ comment?
>
>  Jarno
>
>> On Oct 7, 2016, at 9:17 AM, Bhanuprakash Bodireddy
><bhanuprakash.bodireddy at intel.com> wrote:
>>
>> By reordering the data elements in dpif_upcall structure, pad bytes
>> can be reduced and also a cache line.
>>
>> Before: structure size:768, holes:1, sum padbytes:60, cachelines:12
>> After: structure size:656, holes:1, sum padbytes:4, cachelines:11
>>
>> Signed-off-by: Bhanuprakash Bodireddy
>> <bhanuprakash.bodireddy at intel.com>
>> Signed-off-by: Antonio Fischetti <antonio.fischetti at intel.com>
>> ---
>> lib/dpif.h | 17 +++++++++--------
>> 1 file changed, 9 insertions(+), 8 deletions(-)
>>
>> diff --git a/lib/dpif.h b/lib/dpif.h
>> index a7c5097..4a4bb3d 100644
>> --- a/lib/dpif.h
>> +++ b/lib/dpif.h
>> @@ -779,17 +779,18 @@ const char *dpif_upcall_type_to_string(enum
>> dpif_upcall_type); struct dpif_upcall {
>>     /* All types. */
>>     enum dpif_upcall_type type;
>> -    struct dp_packet packet;       /* Packet data. */
>> -    struct nlattr *key;         /* Flow key. */
>> -    size_t key_len;             /* Length of 'key' in bytes. */
>> -    ovs_u128 ufid;              /* Unique flow identifier for 'key'. */
>> -    struct nlattr *mru;         /* Maximum receive unit. */
>> -    struct nlattr *cutlen;      /* Number of bytes shrink from the end. */
>>
>>     /* DPIF_UC_ACTION only. */
>> -    struct nlattr *userdata;    /* Argument to
>OVS_ACTION_ATTR_USERSPACE. */
>> -    struct nlattr *out_tun_key;    /* Output tunnel key. */
>>     struct nlattr *actions;    /* Argument to OVS_ACTION_ATTR_USERSPACE.
>*/
>> +    struct nlattr *out_tun_key;    /* Output tunnel key. */
>> +    struct nlattr *userdata;    /* Argument to
>OVS_ACTION_ATTR_USERSPACE. */
>> +
>> +    struct nlattr *cutlen;      /* Number of bytes shrink from the end. */
>> +    struct nlattr *mru;         /* Maximum receive unit. */
>> +    ovs_u128 ufid;              /* Unique flow identifier for 'key'. */
>> +    struct dp_packet packet;       /* Packet data. */
>> +    struct nlattr *key;         /* Flow key. */
>> +    size_t key_len;             /* Length of 'key' in bytes. */
>> };
>>
>> /* A callback to notify higher layer of dpif about to be purged, so
>> that
>> --
>> 2.4.11
>>
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