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Date: Thu, 22 Mar 2012 08:09:01 +0100 From: Richard Cochran <richardcochran@...il.com> To: "Keller, Jacob E" <jacob.e.keller@...el.com> Cc: chetan loke <loke.chetan@...il.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "e1000-devel@...ts.sourceforge.net" <e1000-devel@...ts.sourceforge.net>, "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>, "Ronciak, John" <john.ronciak@...el.com>, "john.stultz@...aro.org" <john.stultz@...aro.org>, "tglx@...utronix.de" <tglx@...utronix.de> Subject: Re: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of the timecompare method On Wed, Mar 21, 2012 at 05:06:09PM +0000, Keller, Jacob E wrote: > > I agree with Chetan. I think it would be best to make sure the > correct form of locking is done, as we are providing an interface to > the user. Using a seqlock would allow for preventing the ioctls from > blocking the hardware timestamp code. Okay, you can improve the time stamping path in the driver to avoid contending with callers to clock_gettime. But that will not help the hundreds of clock_gettime callers from contending with each other. > It's a fairly simple change for the gettime function (the most > likely culprit to be hammered) by changing it to use > timecounter_cyc2time function instead of timecounter_read. (as long > as timecounter_read is called at least every 1/2 the system time > overflow, which it should be due to the work task.) > > With that change, then the section use a seqlock (along with the > section for checking hardware timestamps). Other places would do the > full write lock. So, you think that clock_gettime should not read the card's time registers? Richard -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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