linux-kernel - Re: loaded router, excessive getnstimeofday in oprofile

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Date:	Thu, 28 Aug 2008 11:07:20 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	David Miller <davem@...emloft.net>
Cc:	andi@...stfloor.org, rick.jones2@...com, johnpol@....mipt.ru,
	dada1@...mosbay.com, denys@...p.net.lb, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: loaded router, excessive getnstimeofday in oprofile

On Thursday 28 August 2008 10:48, David Miller wrote:
> From: Nick Piggin <nickpiggin@...oo.com.au>
> Date: Thu, 28 Aug 2008 10:45:03 +1000
>
> > On Thursday 28 August 2008 08:39, Andi Kleen wrote:
> > > On Wed, Aug 27, 2008 at 03:18:24PM -0700, David Miller wrote:
> > > > From: Andi Kleen <andi@...stfloor.org>
> > > > Date: Wed, 27 Aug 2008 18:27:35 +0200
> > > >
> > > > > > Those banks really want to crank down on latency - to the point
> > > > > > they start disabling interrupt coalescing.  I bet they'd toss
> > > > > > anything out they could to shave another microsecond.
> > > > >
> > > > > This change would actually likely lower their latency.
> > > >
> > > > They want the timestamps, but they want it to match when the packet
> > > > arrived at their system as closely as is reasonably possible.
> > >
> > > Then they should use hardware time stamps which are increasingly
> > > available (e.g. current Intel e1000 design has them and I expect
> > > others too).
> >
> > Would it make sense to make a new option for these socket timestamps
> > and encourage some apps move over to it?
>
> We don't have support to using these specific hardware provided timestamps
> sources yet, so it's kind of premature to recommend the facility to
> applications. :)

Dang, that was a really badly quoted. I was reading the thread and
got to the end and just fired off my reply from there...

Sorry -- what I meant to ask was, would it make sense to have a new
option to enable time stamp measuring in the socket receive layer
as in the patchset that Andi referenced, but without removing existing
support for early timestamping?

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