[Interest] how to run 21 threads concurrently

Constantin Makshin cmakshin at gmail.com
Thu Oct 4 16:18:56 CEST 2012

Sujan said he uses threads to generate files, so there's some chance that
his task'll be IO-bound and extra threads will actually increase overall

But this is just a guess and running 21 threads on an 8-core CPU is
probably an overkill (unless the task is *really* IO-limited).
On Oct 4, 2012 5:52 PM, "Thiago Macieira" <thiago.macieira at intel.com> wrote:

> On quinta-feira, 4 de outubro de 2012 15.46.57, André Somers wrote:
> > If you think that running 21 threads on an 8 core system will run make
> > your task go faster, then Thiago is right: you don't understand your
> > problem.
> If you run 8 threads on an 8-core system and they use the CPU fully, then
> you're running as fast as you can.
> If you have more threads than the number of processors and if all threads
> are
> ready to be executed, then the OS will schedule timeslices to each thread.
> That means threads get executed and suspended all the time, sometimes
> migrating between processors. That adds overhead.
> If it adds overhead, it's slower. Depending on your OS, it might be
> considerably slower.
> If you do not understand what I said, understand this: there's a reason why
> QtConcurrent runs as many threads as there are processors.
> --
> Thiago Macieira - thiago.macieira (AT) intel.com
>   Software Architect - Intel Open Source Technology Center
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