Re: [patch 1/2] x86_64 page fault NMI-safe

Peter Zijlstra
2010-08-06T11:15:43Z

On Fri, 2010-08-06 at 12:11 +0200, Peter Zijlstra wrote:
> > You need to read the whole trace to find these cookies (even if it is just once
> > at the beginning if you create an index).

Even if you want to index all sync points you can quickly skip through
the file using the sync-distance, after which you'll have, on average,
only 1/2 avg-event-size to read before you find your next sync point.

So suppose you have a 1M sync-distance, and an effective average event
size of 128 bytes, then for a 4G file, you can find all sync points by
only reading ~262144 bytes (not counting for the fact that the pagecache
will bring in full pages, which would result in something like 16M to be
read in total or somesuch -- which, again assumes read-ahead isn't going
to play tricks on you).