Re: [Bug-wget] GSoC15: Speed up Wget's Download Mechanism

[Tim Rühsen]

Am Donnerstag, 30. April 2015, 18:45:05 schrieb Daniel Stenberg:
> On Thu, 30 Apr 2015, Tim Ruehsen wrote:
> > Originally, Gisle talked about CPU cycles, not elapsed time.
> > That is quite a difference...
> 
> Thousands of cycles per invoke * many invokes = measurable elapsed time

Again: That is quite a difference...

1Ghz CPU: 1cycle~1ns, means 1000*1ns = 1us (microsecond). 
But if one packet comes 10ms later (pretty normal on the network) that would 
be equal to ~10 million cycles (equal to about 10.000 calls to 
run_with_timeout, if Gisle's assumptions are right).

How could you distinguish these two, latency and wasted cycles ?

On Linux even the 'time' command is helpful here (if your downloadable is 
large enough to generate a CPU cycle footprint > few ms).
Much better is 'valgrind --tool=callgrind' plus a tool like kcachegrind.

But Gisle is on Windows... I don't know what tools are available there.

Regards, Tim

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