[Gdal-dev] ECW compression - Extremely slow Linux performance

[Frank Warmerdam]

Andrew Larcombe wrote:
> strace'ing gdal_translate gives this:
> 
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
>  35.14    0.357212          14     26030           write
>  24.54    0.249446           9     26948           sched_yield
>  18.41    0.187088           7     25948           gettimeofday
>   9.42    0.095770          17      5505           nanosleep
>   7.40    0.075248           6     12238           _llseek
>   1.68    0.017050          11      1576         1 read
>   1.64    0.016643          65       257           munmap
>   0.46    0.004717          15       317           mprotect
>   0.32    0.003283         657         5           unlink
>   0.29    0.002901          24       119           brk
...
> 
> Do you have any more thoughts on this, or where the problem could lie? 
> It does seem to be making an awfully large number of gettimeofday calls, 
> although maybe this is a red herring?

Andrew,

There are some interesting points for investigation here, but nothing that
seems conclusive to me.  Actually, if I were to check something it would
be all the nanosleep() calls.  This suggests there is a hack somewhere in
the code to "sleep for a little while" to try and avoid some sort of lock
or race condition, but a little sleeping a lot of times can easily result
in the poor cpu utilization we are seeing.

I appologise for not digging into this at my end, but I don't really have
time to do an indepth investigation. And since it has been some time since
3.3RC2, I hate to do a lot of investigation on an old source tree for the
SDK.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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