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

[Mathieu Desnoyers]

* Peter Zijlstra (peterz@xxxxxxxxxxxxx) wrote:
> 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).

How do you distinguish between sync events and random payload data ?

Mathieu


-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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