From: Eric Dumazet <eric.dumazet@gmail.com>
To: Richard Cochran <richardcochran@gmail.com>
Cc: netdev@vger.kernel.org, e1000-devel@lists.sourceforge.net,
Jacob Keller <jacob.e.keller@intel.com>,
Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
John Ronciak <john.ronciak@intel.com>,
John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH net-next 2/2] igb: offer a PTP Hardware Clock instead of the timecompare method
Date: Tue, 13 Dec 2011 04:52:29 +0100 [thread overview]
Message-ID: <1323748349.2583.38.camel@edumazet-laptop> (raw)
In-Reply-To: <20111213034132.GC9604@netboy.at.omicron.at>
Le mardi 13 décembre 2011 à 04:41 +0100, Richard Cochran a écrit :
> On Tue, Dec 13, 2011 at 04:28:52AM +0100, Eric Dumazet wrote:
> >
> > Adding a (shared) spinlock on a multiqueue device is source of extra
> > delay (because of extra cache line trafic), I guess.
> >
> > It seems current code doesnt need a spinlock, maybe it was a bug ?
>
> (I didn't think about the old code. I only deleted it. ;)
>
> The spinlock is needed because reading the 64 bit time value involves
> reading two 32 registers. The first read latches the value. Ditto for
> writing.
>
> In addition, here we have to watch the most significant bit for
> one-to-zero transistion, in order to keep count of the overflow.
>
> It is too bad that we have to take the spinlock for every time stamped
> packet, but it is the hardware's fault for not providing a 64 bit wide
> nanosecond time register.
>
Yes, probably. Are you sure a workaround is not possible, using a
seqlock for synchronization of threads, and two hardware reads ?
Or maybe it doesnt matter at all :)
next prev parent reply other threads:[~2011-12-13 3:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-13 3:00 [PATCH net-next 0/2] [RFC] igb: ptp hardware clock Richard Cochran
2011-12-13 3:00 ` [PATCH net-next 1/2] igb: add PTP Hardware Clock code Richard Cochran
2011-12-25 15:30 ` Richard Cochran
2011-12-13 3:00 ` [PATCH net-next 2/2] igb: offer a PTP Hardware Clock instead of the timecompare method Richard Cochran
2011-12-13 3:28 ` Eric Dumazet
2011-12-13 3:41 ` Richard Cochran
2011-12-13 3:52 ` Eric Dumazet [this message]
2011-12-13 4:40 ` Richard Cochran
2011-12-14 22:33 ` Jesse Brandeburg
2011-12-15 16:12 ` Richard Cochran
2011-12-15 16:46 ` Wyborny, Carolyn
2011-12-25 11:30 ` Richard Cochran
2011-12-25 15:32 ` Richard Cochran
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