netdev - Re: [RFC] dccp ccid-3: High-res or low-res timers?

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Message-ID: <4921C5A1.5030609@cs.ucla.edu>
Date:	Mon, 17 Nov 2008 11:27:29 -0800
From:	Eddie Kohler <kohler@...ucla.edu>
To:	Gerrit Renker <gerrit@....abdn.ac.uk>,
	Leandro Sales <leandroal@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	ian.mcdonald@...di.co.nz, DCCP Mailing List <dccp@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: [RFC] dccp ccid-3: High-res or low-res timers?

Gerrit Renker wrote:
> I would appreciate some advice and insights regarding the use of
> high-resolution timers within a transport protocol, specifically
> DCCP with CCID-3 (RFC 5348).
> 
 > ...
 >
> Summing up, I have doubts that basing CCID-3 will bring advantages and
> would much rather go the other way and (consistently) use lower resolution.
> 
> Thoughts?

I agree.  If one way must be chosen, then choose lower resolution timers.

The biggest potential problem with lower-resolution timers is that a sender's 
rate might be limited, not by network characteristics, but by timer 
resolution.  But DCCP allows a fair amount of burstiness already.  And there 
may be ways to avoid rate limitation in common cases without resorting to 
hrtimers.  For example, a sending application could use a mixture of 
non-blocking system calls, allowing the sending application to "poke" the DCCP 
implementation on every scheduling.

At any rate, it seems worth trying.

Eddie

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