All of lore.kernel.org
 help / color / mirror / Atom feed
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Denny Page <dennypage@me.com>
Cc: Richard Cochran <richardcochran@gmail.com>,
	netdev@vger.kernel.org, Jiri Benc <jbenc@redhat.com>,
	"Keller, Jacob E" <jacob.e.keller@intel.com>,
	Willem de Bruijn <willemb@google.com>
Subject: Re: Extending socket timestamping API for NTP
Date: Mon, 27 Mar 2017 12:13:24 +0200	[thread overview]
Message-ID: <20170327101324.GI8192@localhost> (raw)
In-Reply-To: <89CFCD8E-1A58-48C5-9D6E-99695502CFD9@me.com>

On Fri, Mar 24, 2017 at 10:17:51AM -0700, Denny Page wrote:
> > On Mar 24, 2017, at 02:45, Miroslav Lichvar <mlichvar@redhat.com> wrote:
> > How common is to have link speed changing in normal operation on LAN?
> 
> In my case, it’s currently every few minutes because I’m doing hw timestamp testing. :)
> 
> But this does speak to my point. If it’s cached by the application, the application has to check it regularly to minimize the possibility of bad timestamps. If the link speed doesn’t change, every call by the application is wasted overhead. If it’s cached by the driver, there is no waste, and the stamps are always correct.

At least on the HW I'm testing, reading the link speed from user space
doesn't take much. It's about 10-15x faster than reading the PHC for
instance, which must be done periodically in any case.

> I should have remembered this yesterday... I went and looked at my favorite driver, Intel's igb. Not only is the igb driver already caching link speed, it is also performing timestamp correction based on that link speed.

Isn't the i210 the only NIC for which the correction is actually
implemented? Will this ever be done for all HW with timestamping
support, so that the applications wouldn't have to care about link
speed?

> I believe that timestamp correction, whether it be speed based latency, header -> trailer, or whatever else might be needed later down the line, are properly done in the driver. It’s a lot for the application to try and figure out if it should or should not be doing corrections and what correction to apply. The driver knows.

I agree, but I'm not sure how feasible that is.

-- 
Miroslav Lichvar

  parent reply	other threads:[~2017-03-27 10:13 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-07 14:01 Extending socket timestamping API for NTP Miroslav Lichvar
2017-02-07 17:45 ` Keller, Jacob E
2017-02-07 22:32   ` Willem de Bruijn
2017-02-08 14:18     ` Soheil Hassas Yeganeh
2017-02-27 15:23     ` Miroslav Lichvar
2017-02-28  0:01       ` Willem de Bruijn
2017-02-28  8:26         ` Miroslav Lichvar
2017-02-28 21:05           ` Willem de Bruijn
2017-02-08  1:52   ` Denny Page
2017-02-08  5:27     ` Richard Cochran
2017-02-08  5:48       ` Denny Page
2017-02-08 17:27       ` Denny Page
2017-02-07 18:54 ` Soheil Hassas Yeganeh
2017-02-08 10:14   ` Miroslav Lichvar
2017-02-07 20:37 ` sdncurious
2017-02-08 10:26   ` Miroslav Lichvar
2017-02-08 23:27     ` sdncurious
2017-02-08 23:34     ` sdncurious
2017-02-08  1:18 ` Denny Page
     [not found] ` <CAHoNx58u=Fze4e5V2Wb_LiBhka1Mzny3zOVNfvuzjnmQ4wBO=Q@mail.gmail.com>
2017-02-08  3:06   ` Denny Page
2017-02-09  0:45 ` Denny Page
2017-02-09 11:15   ` Miroslav Lichvar
2017-02-09 20:25   ` Denny Page
2017-02-09  8:02 ` Richard Cochran
2017-02-09 11:09   ` Miroslav Lichvar
2017-02-09 19:42     ` sdncurious
2017-02-09 20:37       ` Denny Page
2017-02-10  0:33       ` Denny Page
2017-02-10 18:55         ` Denny Page
2017-03-23 16:21     ` Miroslav Lichvar
2017-03-23 18:54       ` Denny Page
2017-03-23 19:07       ` Richard Cochran
2017-03-24  7:25         ` Miroslav Lichvar
     [not found]       ` <6121D504-288F-4C9B-9AB3-D1C8292965D5@me.com>
2017-03-24  9:45         ` Miroslav Lichvar
2017-03-24 17:17           ` Denny Page
2017-03-24 18:52             ` Keller, Jacob E
2017-03-27 10:13             ` Miroslav Lichvar [this message]
2017-03-27 14:29               ` Richard Cochran
2017-03-27 16:25                 ` Denny Page
2017-03-27 18:28                   ` Richard Cochran
2017-03-27 19:18                     ` Denny Page
2017-03-27 20:58                       ` Richard Cochran
2017-03-27 21:20                         ` Denny Page
2017-03-27 19:21                     ` Denny Page
2017-03-27 19:21                     ` Denny Page
     [not found]                     ` <5FD283AB-39DE-4A9D-902A-BA5F0F0B62A3@me.com>
2017-03-27 21:00                       ` Richard Cochran
2017-03-24  9:55         ` Jiri Benc

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20170327101324.GI8192@localhost \
    --to=mlichvar@redhat.com \
    --cc=dennypage@me.com \
    --cc=jacob.e.keller@intel.com \
    --cc=jbenc@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=richardcochran@gmail.com \
    --cc=willemb@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.