netdev - Re: Using jiffies for tcp_time

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Message-ID: <CAA93jw7MU8PjFk-UX864STSBp2SjjjivmfpRiPhaQ2kxZLu2sA@mail.gmail.com>
Date:	Fri, 25 May 2012 17:17:42 +0100
From:	Dave Taht <dave.taht@...il.com>
To:	Chris Friesen <chris.friesen@...band.com>
Cc:	Srećko Jurić-Kavelj 
	<srecko.juric-kavelj@....hr>, netdev@...r.kernel.org
Subject: Re: Using jiffies for tcp_time_stamp?

On Fri, May 25, 2012 at 4:58 PM, Chris Friesen
<chris.friesen@...band.com> wrote:
> 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.

I would be interested in someone doing that experiment in light of the
codel work.
>
> Chris
>
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Dave Täht
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