netdev - Re: [PATCH net-next 3/7] net-timestamp: tx timestamp without payload

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Date:	Wed, 25 Jun 2014 17:22:09 -0400
From:	Willem de Bruijn <willemb@...gle.com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next 3/7] net-timestamp: tx timestamp without payload

On Wed, Jun 25, 2014 at 1:16 AM, Richard Cochran
<richardcochran@...il.com> wrote:
> On Tue, Jun 24, 2014 at 11:43:48AM -0400, Willem de Bruijn wrote:
>> Applications receive tx timestamps from the kernel by reading the
>> original packet from the socket error queue with sendmsg() and
>> processing an ancillary data item that holds the timestamps.
>>
>> If the application is only interested in the timestamp, then looping
>> the whole packet back up to userspace wastes socket buffer space
>> (SO_RCVBUF). This is especially important when the same packet is
>> enqueued repeatedly with multiple timestamps.
>>
>> This patch adds a socket option to loop the timestamp on top of an
>> empty packet instead of a clone of the original.
>
> This makes sense. In practice the looped buffer is totally useless,
> due to the fact that many NICs can only handle one outstanding
> transmit time stamp. Applications must make sure they only send one
> packet at a time if they want every packet time stamped.
>
>> diff --git a/include/net/sock.h b/include/net/sock.h
>> index 32cd1be..df7bde0 100644
>> --- a/include/net/sock.h
>> +++ b/include/net/sock.h
>> @@ -690,6 +690,7 @@ enum sock_flags {
>>       SOCK_TIMESTAMPING_SOFTWARE,     /* %SOF_TIMESTAMPING_SOFTWARE */
>>       SOCK_TIMESTAMPING_RAW_HARDWARE, /* %SOF_TIMESTAMPING_RAW_HARDWARE */
>>       SOCK_TIMESTAMPING_SYS_HARDWARE, /* %SOF_TIMESTAMPING_SYS_HARDWARE */
>> +     SOCK_TIMESTAMPING_OPT_TX_NO_PAYLOAD, /* %SOF_TIMESTAMPING_OPT_TX_NO_PAYLOAD */
>
> That is a bit of a mouthful. How about something like:
>
>  SOCK_TIMESTAMPING_PLAIN_TS
>  SOCK_TIMESTAMPING_BARE_TS
>  SOCK_TIMESTAMPING_TSONLY

Ack. I'll pick a shorter name. This also exceeded 80 chars.
>
>
> Thanks,
> Richard
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