From: Richard Cochran <richardcochran@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: e1000-devel@lists.sourceforge.net, netdev@vger.kernel.org,
John Ronciak <john.ronciak@intel.com>,
John Stultz <john.stultz@linaro.org>,
Jacob Keller <jacob.e.keller@intel.com>,
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 04:41:33 +0100 [thread overview]
Message-ID: <20111213034132.GC9604@netboy.at.omicron.at> (raw)
In-Reply-To: <1323746932.2583.33.camel@edumazet-laptop>
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.
Richard
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next prev parent reply other threads:[~2011-12-13 3:41 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 [this message]
2011-12-13 3:52 ` Eric Dumazet
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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