RE: [RFC PATCH 00/13] hardware time stamping + igb example implementation

Ohly, Patrick
2008-11-13T15:53:39Z

Oliver Hartkopp wrote:
>Andi Kleen wrote:
>>Eric Dumazet wrote:
>>> I threw a "crazy idea", that can be changed if necessary, say with a
>>> cookie
>>> that identifies the slot in NIC driver structure. O(1) lookup if
>>> really needed.
>>
>> I think "crazy" describes it well because it would be a lot of dubious
>> and likely not performing well effort just to save 8 bytes.
>>
>
> The crazy idea from Eric looks easier and more clearly to me than the
> discussed patch set from Patrick Ohly - but i wonder if we should give a
> separate hw timestamp a try ...

For reasons that have been mentioned already here (some hardware can
time stamp every packet, new use cases) I think it would be important
to have the hwtstamp information right in the skb. I can change the
patch series so that it uses one additional ktime_t hwtstamp field; give
me a few days, I'm currently traveling.

> I know Patrick is not a friend of a CONFIG option here. But when we make
> it right HW timestamp could only be disabled on CONFIG_EMBEDDED or
> something like that.

I'm not a friend of a config option because it was suggested that
hardware tstamps should off on *standard* kernels. That's of little
use for users of unmodified distributions who want to run PTP.

If the feature is only disabled on special distributions, then I really
don't mind, but at the same time I wonder whether these distributions
are performance sensitive enough to care about the additional field.

Bye, Patrick