netdev - Re: Using jiffies for tcp_time

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Date:	Fri, 25 May 2012 09:58:40 -0600
From:	Chris Friesen <chris.friesen@...band.com>
To:	Srećko Jurić-Kavelj 
	<srecko.juric-kavelj@....hr>
CC:	netdev@...r.kernel.org
Subject: Re: Using jiffies for tcp_time_stamp?

On 05/22/2012 11:21 AM, Srećko Jurić-Kavelj wrote:

> By looking at the code it's clear that the time stamping is done with
> jiffies, and my kernel has CONFIG_HZ=100.
>
> I understand that this is for performance reasons (and the RTT
> smoothing filter is implemented with bit shifting operations), but
> would using a more precise time stamp have significant impact on
> performance? Since RTT is used to compute RTO, wouldn't there be any
> benefits of having more accurate estimate of this value?

I don't know if it would make any difference to the tcp algorithms, but 
certainly on some architectures you can get a fast and accurate hardware 
timestamp.

Chris
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