netdev - Re: [PATCH v5 net-next] tcp: switch rtt estimations to usec resolution

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Date:	Mon, 24 Feb 2014 17:11:07 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	Julian Anastasov <ja@....bg>, David Miller <davem@...emloft.net>,
	Yuchung Cheng <ycheng@...gle.com>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Larry Brakmo <brakmo@...gle.com>
Subject: Re: [PATCH v5 net-next] tcp: switch rtt estimations to usec
 resolution

On Mon, 2014-02-24 at 15:51 -0800, Stephen Hemminger wrote:

> 
> The original reason I kept ms resolution and added the flag was
> that accessing high resolution time is expensive for systems where
> TSC is not stable.  Google may live in a world of SMP systems with
> good X86 CPUs with working TSC, but other architectures and system
> config's may have non-working TSC.

Well, it seems we now have alternatives to ktime_get() that were
probably not yet there at the time you made this choice ?

We only want a reasonable alternative to jiffies based measures,
we do not need ultra precise and synchronized clocks.

I'll redo tests with hpet clocksource, and local_clock()

Thanks



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