Re: [Linuxptp-users] Expected throughput of the ptp4l

[Chandra M. <sma...@al...>]

Hi Richard,

>From my interactions with the customer as an architect, I could see the need for 512 syncs per second, due to high-end frequency correction (think of a 1588 application to replace/compete with SyncE applicationIn a pure telecom application, high frequency Sync packets might encroach into datatraffic. However, in back-hauling (be it telecom or networking), where high-throughput is already a given parameter, high frequency Sync packets are desirable for frequency corrections. ). On offset correction, I can take liberties on DelayReq sets.

Do we have the performance metrics of the ptp4l in a standard Linux OS? At what rates of the packets, does the stack break down? If we have any data, it will be good for us to know. If you have any ideas as to how to arrive at the numbers, please let me know - I can try it out with the system at my hand.

Thanking you in anticipation,
Regards,
Chandra

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-----Original Message-----
From: Richard Cochran [mailto:ric...@gm...]
Sent: Wednesday, March 18, 2015 2:06 AM
To: Chandra Mallela
Cc: Miroslav Lichvar; lin...@li...
Subject: Re: [Linuxptp-users] Expected throughput of the ptp4l

On Tue, Mar 17, 2015 at 05:28:45PM +0000, Chandra Mallela wrote:
> As for 'what is that supposed to achieve?', in ideal scenario, targeting 50pbb for CDMA is what I look at. I am further trying to analyze SyncE requirements from 1588 perspective, which seems too tough at this moment due to OS scheduling jitter itself.
>
> Please correct me as appropriate and pour in your thoughts.

So 50 pbb means 50 nanoseconds.  That should be attainable with a more moderate Sync rate, but it depends on your hardware time stamping resolution, etc.

With SyncE, you need to hack ptp4l *not* to touch the frequency adjustment.  I have some patches in the works for this, but you can change the code yourself in the mean time.

Using SyncE and the default 1 Hz Sync, I have seen two nodes synchronized to within 8 nanoseconds (the clock period of those systems).

So, I really, truly don't see the need for 512 Syncs per second.  But if you want run that rate, then you are going to have to optimize your system, especially WRT to real time response, as I said before.

Thanks,
Richard


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