From: Thomas Gleixner <tglx@linutronix.de>
To: Johannes Berg <johannes@sipsolutions.net>
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 16:09:32 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.10.1406121605470.5170@nanos> (raw)
In-Reply-To: <1402564914.8095.9.camel@jlt4.sipsolutions.net>
On Thu, 12 Jun 2014, Johannes Berg wrote:
> On Thu, 2014-06-12 at 10:57 +0200, Thomas Gleixner wrote:
>
> > > > 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?
> >
> > Indeed. clock monotonic is the appropriate one for measurements.
>
> And that's what we had here with ktime_get_ts()? I thought so, just
> making sure.
>
> > > > 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?
> >
> > You have the same problem then, just at a different place:
> >
> > ts = ktime_get();
> >
> > settimeofday()
> > offset_mono_to_real = new value;
> >
> > userts = mono_to_real(ts);
>
> Right. I'm not really sure if that's an issue though.
>
> > But maybe that's not a real issue, as ktime_get_real() can race with
> > settimeofday() or NTP as well.
> >
> > ts = ktime_get_real();
> > settimeofday();
> > userts = ts;
> >
> > So the user might see a weird timestamp for a packet, which cannot be
> > correlated with the user space gettimeofday().
>
> Right, once settimeofday() is called the timestamps from before/during
> it can't really be correlated any more.
>
> This is part of the userspace API already, but might it have been better
> to expose the monotonic clock, since userspace can also get at it? Not
> sure.
>
> Either way it's an issue I guess; however I'm thinking your patch is
> making it worse for the measurement in this particular code (where the
> userspace issue doesn't come in, it should never be accessible there)
Fair enough. Still the timespec is silly. Here is an updated version.
Thanks,
tglx
------------------>
Subject: net: Mac80211: Remove silly timespec dance
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 11 Jun 2014 23:59:18 -0000
Converting time from one format to another seems to give coders a warm
and fuzzy feeling.
Use the proper interfaces.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: John W. Linville <linville@tuxdriver.com>
---
net/mac80211/status.c | 7 ++-----
net/mac80211/tx.c | 5 +----
2 files changed, 3 insertions(+), 9 deletions(-)
Index: tip/net/mac80211/status.c
===================================================================
--- tip.orig/net/mac80211/status.c
+++ tip/net/mac80211/status.c
@@ -473,8 +473,6 @@ static void ieee80211_tx_latency_end_msr
struct sta_info *sta,
struct ieee80211_hdr *hdr)
{
- ktime_t skb_dprt;
- struct timespec dprt_time;
u32 msrmnt;
u16 tid;
u8 *qc;
@@ -506,9 +504,8 @@ static void ieee80211_tx_latency_end_msr
tx_lat = &sta->tx_lat[tid];
- ktime_get_ts(&dprt_time); /* time stamp completion time */
- skb_dprt = ktime_set(dprt_time.tv_sec, dprt_time.tv_nsec);
- msrmnt = ktime_to_ms(ktime_sub(skb_dprt, skb_arv));
+ /* Calculate the latency */
+ msrmnt = ktime_to_ms(ktime_sub(ktime_get(), skb_arv);
if (tx_lat->max < msrmnt) /* update stats */
tx_lat->max = msrmnt;
Index: tip/net/mac80211/tx.c
===================================================================
--- tip.orig/net/mac80211/tx.c
+++ tip/net/mac80211/tx.c
@@ -1767,15 +1767,12 @@ fail:
static void ieee80211_tx_latency_start_msrmnt(struct ieee80211_local *local,
struct sk_buff *skb)
{
- struct timespec skb_arv;
struct ieee80211_tx_latency_bin_ranges *tx_latency;
tx_latency = rcu_dereference(local->tx_latency);
if (!tx_latency)
return;
-
- ktime_get_ts(&skb_arv);
- skb->tstamp = ktime_set(skb_arv.tv_sec, skb_arv.tv_nsec);
+ skb->tstamp = ktime_get();
}
/**
next prev parent reply other threads:[~2014-06-12 14:10 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
2014-06-12 8:57 ` Thomas Gleixner
2014-06-12 9:21 ` Johannes Berg
2014-06-12 14:09 ` Thomas Gleixner [this message]
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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