Re: do_gettimeofday

[Mitchell Blank Jr <mitch@sfgoth.com>]

David S. Miller wrote:
> 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 definately the worst case.  You could have each CPU periodically
store its current {tsc,timeval} tuple in a per-cpu location and extrapolate
from that.

> That's really expensive and probably
> do_gettimeofday() is going to be faster in the long run compared to
> such a scheme.

It all depends on what percentage of skb's have ->stamp computed on a
CPU different from the one they came it on.  For the common users of
->stamp won't they have stayed on the same CPU?  The worst case of
doing a cross-cpu-call should only happen relatively rarely.

-Mitch