Subject: Re: [PATCH] Bound TSO defer time (resend)

From: Stephen Hemminger <[email-masked]>
Date: Wed, 18 Oct 2006 09:40:23 -0700

On Wed, 18 Oct 2006 17:37:36 +0200
Andi Kleen <[email-masked]> wrote:

> On Tuesday 17 October 2006 06:18, John Heffner wrote:
> > Stephen Hemminger wrote:
> > > On Mon, 16 Oct 2006 20:53:20 -0400 (EDT)
> > > John Heffner <[email-masked]> wrote:
> > 
> > >> This patch limits the amount of time you will defer sending a TSO segment
> > >> to less than two clock ticks, or the time between two acks, whichever is
> > >> longer.
> > 
> > > 
> > > Okay, but doing any timing on clock ticks makes the behavior dependent
> > > on the value of HZ which doesn't seem desirable. Should this be based
> > > on RTT or a real-time values?
> > 
> > It would be nice to use a high res clock so you don't depend on HZ, but 
> > this is still expensive on most SMP arch's as I understand it.
> 
> You can always use xtime. It doesn't have better solution than jiffies
> though, but it gives you real time.
> 
> Drawback is that there is some work towards tickless kernels and with
> that xtime will be more expensive again. But hopefully not by that much.
> 
> -Andi

Actually the thing to use now is ktime.  It would then be compatiable
with hrtimers. But it seems a bit of overkill in this case.

-- 
Stephen Hemminger <[email-masked]>