Subject: Re: [RFC v3 net-next 08/18] net: SO_TXTIME: Add clockid and drop_if_late params

From: Miroslav Lichvar <[email-masked]>
Date: Thu, 8 Mar 2018 12:37:22 +0100

On Wed, Mar 07, 2018 at 02:45:45PM -0800, Eric Dumazet wrote:
> On Wed, 2018-03-07 at 13:52 -0800, Jesus Sanchez-Palencia wrote:
> > > Do we really need 32 bits for a clockid_t ?
> > 
> > There is a 2 bytes hole just after tc_index, so a u16 clockid would
> > fit
> > perfectly without increasing the skbuffs size / cachelines any
> > further.

> Not convincing really :/
> 
> Next big feature needing one bit in sk_buff will add it, and add a
> 63bit hole.

Would it be possible to put the clockid in skb_shared_info? If that's
technically difficult or does not make sense, I'm ok with the clockid
being a socket option.

If a packet is sent immediately after changing the clockid via
setsockopt(), will it be still guaranteed that the packet is
restricted by the new id?

> Why do we _really_ need dynamic clocks being supported in core
> networking stack, other than 'that is needed to send 2 packets per
> second with precise departure time and arbitrary user defined clocks,
> so lets do that, and do not care of the other 10,000,000 packets we
> receive/send per second'

Well, I'd not expect it to be a common use case, but a public NTP
server could be sending millions of packets per second in traffic
peaks (typically at *:00:00) over multiple interfaces.

-- 
Miroslav Lichvar