Re: [Linuxptp-users] Intel NICs PTP Performance Comparison

[Keller, J. E <jac...@in...>]

> -----Original Message-----
> From: Keller, Jacob E
> Sent: Thursday, June 17, 2021 5:04 PM
> To: 'Dale Smith' <dal...@gm...>; Joseph Matan
> <jos...@gm...>
> Cc: lin...@li...
> Subject: RE: [Linuxptp-users] Intel NICs PTP Performance Comparison
> 
> 
> 
> > -----Original Message-----
> > From: Dale Smith <dal...@gm...>
> > Sent: Thursday, June 17, 2021 3:04 PM
> > To: Joseph Matan <jos...@gm...>
> > Cc: lin...@li...
> > Subject: Re: [Linuxptp-users] Intel NICs PTP Performance Comparison
> >
> > So how in the would could *more* traffic cause a *smaller* delay?
> >
> 
> EEE low power ethernet kicking in, which puts the device into a low power state
> that has a higher latency to wake up. You could check "ethtool --show-eee" to see
> if the device supports it and what the status is.
> 

I missed that you ruled out EEE already. I wonder if i218 supports it without supporting the options to disable it though.... I'm not certain.

Thanks,
Jake

> > Very curious.
> >
> > Wild Guess, maybe interrupt coalescing is going on, and with more
> > packets, it's actually responding sooner?
> 
> This is unlikely, since timestamps are captured in hardware, so I don't think it
> should impact the latency with regards to the actual timestamps.
> 
> >
> > Another guess, that somehow the determination of the timestamps are
> > just plain wrong.  Like maybe they were fudged to some value while
> > under heavy load, and are way more off when under light load?
> >
> 
> I don't think this is the case for Intel devices.
> 
> > Just guesses as I said.  I don't do 1588 much anymore, but this is
> > very intriguing.  Please report back if you ever get to the bottom of
> > this.
> >
> > -Dale
> >
> >
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