Subject: Re: do_gettimeofday

From: "David S. Miller" <[email-masked]>
Date: Fri, 3 Oct 2003 01:27:54 -0700

On Fri, 3 Oct 2003 01:26:42 -0700
Mitchell Blank Jr <[email-masked]> wrote:

> Are there any common cases where skb->stamp is looked at more than
> once?

Yes, the packet scheduler can cause this to happen.

>If so I might recommend changing the API to be more like:
> 
> 	const struct timeval *skb_timestamp(struct skbuff *skb);

Please no, making this a SKB or networking specific interface
make it nearly valueless and we might as well just stay with the
stuff we have.

> > Platforms with inter-cpu TSC synchronization issues will have some
> > troubles doing the same trick too, because one must handle properly
> > the case where the fast timestamp is converted to a timeval on a different
> > cpu on which the fast timestamp was recorded.
> 
> Yeah, you'd probably have something like

Doesn't work as-is.  You'd have to not only store the timestamp and
the cpu it was stored on, but also cross-call to that cpu to compute
the correct timeval.  That's really expensive and probably
do_gettimeofday() is going to be faster in the long run compared to
such a scheme.