From: Johannes Berg <johannes@sipsolutions.net>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
John Stultz <john.stultz@linaro.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
"John W. Linville" <linville@tuxdriver.com>,
linux-wireless@vger.kernel.org,
Stephen Hemminger <shemminger@linux-foundation.org>,
netdev <netdev@vger.kernel.org>
Subject: Re: net_timedelta() affected by settimeofday() (was: [patch 12/13] net: mac80211: Remove silly timespec dance)
Date: Thu, 12 Jun 2014 10:39:59 +0200 [thread overview]
Message-ID: <1402562399.8095.5.camel@jlt4.sipsolutions.net> (raw)
In-Reply-To: <1402562114.8095.3.camel@jlt4.sipsolutions.net> (sfid-20140612_103558_525847_209A5C98)
On Thu, 2014-06-12 at 10:35 +0200, Johannes Berg wrote:
> +netdev, Stephen
Well, stupid me. Fixing that netdev address.
> On Thu, 2014-06-12 at 10:19 +0200, Thomas Gleixner wrote:
> > On Thu, 12 Jun 2014, Johannes Berg wrote:
> >
> > > On Wed, 2014-06-11 at 23:59 +0000, Thomas Gleixner wrote:
> > >
> > > > + msrmnt = ktime_to_ms(net_timedelta(skb_arv));
> > >
> > > This is probably more of a question about net_timedelta(), but is
> > > ktime_get_real() really appropriate for duration measurements? Isn't
> > > that non-monotonic?
> >
> > Well, it's monotonic, but might be affected by settimeofday().
>
> Right, but isn't that odd? Suddenly your delay measurement here might be
> minutes, hours, or years if you settimeofday() between timestamping and
> calculating the delta. That seems very strange to me, why would that be
> the right behaviour in any way?
>
> Now, it seems that there are only two current users of net_timedelta()
> (in DCCP) so perhaps it's not too late to change some of this?
>
> Maybe in general the skb timestamp should be based on a different clock
> and only adjusted to real time when used in userspace?
next prev parent reply other threads:[~2014-06-12 8:40 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-11 23:59 [patch 00/13] time: Tree wide cleanup of interfaces and crap Thomas Gleixner
2014-06-11 23:59 ` [patch 01/13] acct: Use ktime_get_ts() Thomas Gleixner
2014-06-21 20:36 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2014-06-11 23:59 ` [patch 02/13] tsacct: " Thomas Gleixner
2014-06-21 20:37 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2014-06-11 23:59 ` [patch 03/13] delayacct: " Thomas Gleixner
2014-06-21 20:36 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2014-06-11 23:59 ` [patch 05/13] sound: " Thomas Gleixner
2014-06-12 10:42 ` Takashi Iwai
2014-06-12 10:51 ` Thomas Gleixner
2014-06-12 10:59 ` Takashi Iwai
2014-06-11 23:59 ` [patch 04/13] net: mac80211: " Thomas Gleixner
2014-06-12 6:53 ` Johannes Berg
2014-06-12 9:03 ` Luis R. Rodriguez
2014-06-12 9:51 ` [Cocci] " Julia.Lawall
2014-06-12 10:49 ` Thomas Gleixner
2014-06-11 23:59 ` [patch 06/13] sound: intel8x0: Use ktime and ktime_get() Thomas Gleixner
2014-06-11 23:59 ` [patch 08/13] firewire: Use ktime_get_ts() Thomas Gleixner
2014-06-12 12:35 ` Stefan Richter
2014-06-12 14:12 ` Thomas Gleixner
2014-06-21 20:37 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2014-06-11 23:59 ` [patch 07/13] kdb: " Thomas Gleixner
2014-06-21 20:37 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2014-06-11 23:59 ` [patch 10/13] time: Remove do_posix_clock_monotonic_gettime() Thomas Gleixner
2014-06-11 23:59 ` [patch 09/13] fork: Use ktime_get_ts() Thomas Gleixner
2014-06-21 20:37 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2014-06-11 23:59 ` [patch 11/13] wireless: mwifiex: Use the proper interfaces Thomas Gleixner
2014-06-12 3:22 ` Bing Zhao
2014-06-12 8:31 ` [patch V2] " Thomas Gleixner
2014-06-12 8:38 ` Johannes Berg
2014-06-13 18:28 ` Bing Zhao
2014-06-11 23:59 ` [patch 12/13] net: mac80211: Remove silly timespec dance Thomas Gleixner
2014-06-12 6:49 ` Johannes Berg
2014-06-12 8:19 ` Thomas Gleixner
2014-06-12 8:35 ` net_timedelta() affected by settimeofday() (was: [patch 12/13] net: mac80211: Remove silly timespec dance) Johannes Berg
2014-06-12 8:39 ` Johannes Berg [this message]
2014-06-12 8:57 ` Thomas Gleixner
2014-06-12 9:21 ` Johannes Berg
2014-06-12 14:09 ` Thomas Gleixner
2014-06-13 17:58 ` Johannes Berg
2014-06-11 23:59 ` [patch 13/13] tomoyo: Use sensible time interface Thomas Gleixner
2014-06-12 0:08 ` John Stultz
2014-06-12 0:22 ` Thomas Gleixner
2014-06-12 0:28 ` John Stultz
2014-06-12 0:36 ` Thomas Gleixner
2014-06-12 11:53 ` Tetsuo Handa
2014-06-21 20:37 ` [tip:timers/core] " tip-bot for Thomas Gleixner
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