[Fkt-devel] performance issues in fxt

[François Trahay]

Dear all,
I'm using fxt in eztrace and I am experiencing some performance issues due to 
the way fxt_next_ev reads traces.
From my experience, each call to fxt_next_ev take approx. 2µs. Since I need to 
browse traces consisting of millions of events (and these are 'small' traces), 
it becomes prohibitive.

Actually fxt_next_ev calls 'read' several times, leading to a large overhead. 
I managed to modify it so it reads 4KB blocks (reducing the number of calls to 
read and thus the total overhead) and the performance increases a lot: each 
call to fxt_next_ev now cost approx 200ns.

My patch is only lightly tested and this method restricts fxt features: 
fxt_rewind becomes unavailable (but, it could be possible to reimplement it) 
and calls to fxt_next_ev isn't thread-safe anymore (but adding thread-safety 
should'nt be too hard).
Once these issues solved, do you think it could be integrated to fxt ? An 
option could be added at fxt initialization to enable/disable the feature.

François

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