From: Richard Cochran <richardcochran@gmail•com>
To: Chad Reese <kreese@cavium•com>
Cc: Willem de Bruijn <willemb@google•com>,
netdev@vger•kernel.org, David Miller <davem@davemloft•net>,
Eric Dumazet <eric.dumazet@gmail•com>,
Stephen Hemminger <stephen@networkplumber•org>,
Chad Reese <kreese@caviumnetworks•com>,
David Daney <david.daney@cavium•com>
Subject: Re: [PATCH net-next v2 1/8] net-timestamp: explicit SO_TIMESTAMPING ancillary data struct
Date: Mon, 7 Jul 2014 22:11:56 +0200 [thread overview]
Message-ID: <20140707201156.GA10265@localhost.localdomain> (raw)
In-Reply-To: <53BAF8AC.6010907@cavium.com>
On Mon, Jul 07, 2014 at 12:44:44PM -0700, Chad Reese wrote:
>
> A hardware timer used for ethernet timestamps is completely
> independent from the kernel's software view of time. Since the
> hardware timestamps are only exposed in the driver, how can they be
> correlated with system time? If the driver doesn't do it, then
> nobody else knows how.
Um, implement a PTP Hardware Clock device?
Don't reimplement clock servos in your driver. Instead, leave that to
the PTP stack (like using linuxptp's phc2sys).
> For Octeon, you can optionally use the hardware timestamp as the
> system clock reference. Most people don't, but it is the only way to
> get the system time to be accurate. 1588 can synchronize two Octeon
> boards to less than 1ns for the hardware timer. The Linux software
> timers is always farther off.
1588 cannot synchronize boards unless you expose the clock to the
userland PTP stack. Why don't you do that?
Thanks,
Richard
next prev parent reply other threads:[~2014-07-07 20:12 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-03 19:39 net-timestamp: MSG_TSTAMP flags and bytestream support Willem de Bruijn
2014-07-03 19:39 ` [PATCH net-next v2 1/8] net-timestamp: explicit SO_TIMESTAMPING ancillary data struct Willem de Bruijn
2014-07-05 20:10 ` Richard Cochran
2014-07-18 15:54 ` Willem de Bruijn
2014-07-05 20:18 ` Richard Cochran
2014-07-07 15:34 ` Willem de Bruijn
2014-07-07 18:47 ` Richard Cochran
2014-07-07 19:14 ` Willem de Bruijn
2014-07-07 19:44 ` Chad Reese
2014-07-07 20:11 ` Richard Cochran [this message]
2014-07-07 21:03 ` Chad Reese
2014-07-08 6:04 ` Richard Cochran
2014-07-08 7:42 ` Chad Reese
2014-07-08 9:41 ` Richard Cochran
2014-07-10 15:36 ` Willem de Bruijn
2014-07-07 20:18 ` Richard Cochran
2014-07-07 21:08 ` Chad Reese
2014-07-08 5:49 ` Richard Cochran
2014-07-08 6:08 ` Richard Cochran
2014-07-03 19:39 ` [PATCH net-next v2 2/8] net-timestamp: MSG_TSTAMP one-shot tx timestamps Willem de Bruijn
2014-07-03 19:39 ` [PATCH net-next v2 3/8] net-timestamp: tx timestamp without payload Willem de Bruijn
2014-07-03 19:39 ` [PATCH net-next v2 4/8] net-timestamp: TCP timestamping Willem de Bruijn
2014-07-03 19:39 ` [PATCH net-next v2 5/8] net-timestamp: ACK timestamp for bytestreams Willem de Bruijn
2014-07-03 19:39 ` [PATCH net-next v2 6/8] net-timestamp: ENQ timestamp on enqueue to traffic shaping layer Willem de Bruijn
2014-07-03 19:39 ` [PATCH net-next v2 7/8] net-timestamp: expand documentation Willem de Bruijn
2014-07-05 20:14 ` Richard Cochran
2014-07-07 15:40 ` Willem de Bruijn
2014-07-03 19:39 ` [PATCH net-next v2 8/8] net-timestamp: SOCK_RAW and PING timestamping Willem de Bruijn
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