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

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

Hi,

The issue isn't the actual network, but the fact of how transmit
timestamps are are returned. The stack requests a particular packet to
be timestamped, then the driver and device have to send it. Once sent,
driver and device determine the transmission time, usually via some set
of registers, and then have to report this information to the userspace
again. Most devices only support timestamping a few packets at a time,
some even only one. Thus, when you transmit too many syncs too fast, you
can lose transmit timestamps. Even if you don't lose them, they may not
be returned to ptp4l process in time.

LinuxPTP is very careful, and causes a full reset when it loses a
timestamp. Theoretically you could have it keep trying until you got
more failures, but it becomes difficult to say for sure why you lost a
timestamp and whether resetting is better than not.

Regards,
Jake

On Tue, 2015-03-17 at 16:15 +0000, Chandra Mallela wrote:
>  
> 
>  
> 
> Hi Friends,
> 
>  
> 
> Do we have any performance numbers for the ptp4l stack performance on
> a 10Gbps link? When I increase the sync packet frequency to 512 and
> the DelayReq packet frequency to 512, I see many synchronization
> faults, meaning that the ptp4l runs for some time, faces
> synchronization faults, resumes the sync operation, faces the sync
> faults and resumes the operation showing a lot of instability in the
> overall ptp stack operation.
> 
>  
> 
> Is it due to the limitation from the stack performance as the HW
> supports a 10G link? The 512 packets per sync and 512 packet sets of
> {DelayReq, DelayResp} donot occupy even 1% of the 10Gbps bandwidth. 
> 
>  
> 
> Could you elaborate your experience with the ptp4l performance?
> 
>  
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> Thanking you in anticipation,
> 
> Regards,
> 
> Chandra
> 
>  
> 
> © : 0175508142
> 
> (O): 701.6412
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>  
> 
> “Knowledge speaks, Wisdom listens”
> 
>  
> 
> 
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> 
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