netdev - RE: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of the timecompare method

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Message-ID: <02874ECE860811409154E81DA85FBB580DC769@ORSMSX105.amr.corp.intel.com>
Date:	Tue, 27 Mar 2012 20:58:21 +0000
From:	"Keller, Jacob E" <jacob.e.keller@...el.com>
To:	chetan loke <loke.chetan@...il.com>
CC:	Richard Cochran <richardcochran@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"john.stultz@...aro.org" <john.stultz@...aro.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: RE: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of
 the timecompare method

> -----Original Message-----
> From: chetan loke [mailto:loke.chetan@...il.com]
> Sent: Tuesday, March 27, 2012 11:52 AM
> To: Keller, Jacob E
> Cc: Richard Cochran; netdev@...r.kernel.org; e1000-
> devel@...ts.sourceforge.net; Kirsher, Jeffrey T; Ronciak, John;
> john.stultz@...aro.org; tglx@...utronix.de
> Subject: Re: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of the
> timecompare method
> 
> On Tue, Mar 27, 2012 at 2:43 PM, chetan loke <loke.chetan@...il.com> wrote:
> > On Tue, Mar 27, 2012 at 2:29 PM, Keller, Jacob E
> > <jacob.e.keller@...el.com> wrote:
> >
> >>>
> >>
> >> It isn't so much about performance gains as it is about preventing
> >> poorly written user apps from stalling the clean descriptor routines.
> >> I am working on a test case that should prove whether this is even an
> >> issue (at least with ixgbe). Once I have data on that it can be
> >> determined if the extra lock would alleviate it. The conceptual issue
> >> is that spamming get-time could cause the clean tx/rx irq routines to
> >> stall inside the interrupt for too long. (thereby not freeing up
> >> descriptors on the ring to
> >
> > What would be interesting to see is something like:
> >
> > 1) App1(getter/setter calls), executed '1000' ioctls per sec on eth0.
> > Other 'M' apps(execute just get calls), where M = 1 .. 10(?). And one
> > buggy app executed - 10K getter calls per sec.
> >
> > 2) eth0 receives PTP traffic and also around 80-90%(link rate)
> > regular/mixed traffic.
> >
> > And BTW, eth0 is the management IP.
> >
> > While the test is running, if we are still able to reach the host and
> > manage it via SSH then we can stop being paranoid.
> >
> >
> 
> Guys please correct me if I'm wrong but if RPS/RFS is enabled then at a
> minimum we would need "N * 2" apps (where N == num_cpus). That way there will
> be contention w/ the completions and we will be able to see the real effect?
> 
> Chetan

I think we could see contention regardless because the spinlock doesn't guarantee the ordering of who gets it next.

I am not sure. But I will try and set something like this up. However, I do think that many get-set calls is pretty high for even a 'highly' loaded system. Though the buggy app for sure is possible.

Here is what I am thinking as a test case. Linuxptp running normally with a higher sync rate than once per second, plus a 'buggy' app which will try to infinitely thread the gettime calls. I hope to have something like this working soon.

- Jake