[Interest] how to run 21 threads concurrently
sujan.dasmahapatra at gmail.com
Thu Oct 4 16:31:41 CEST 2012
Thanks Thiago for you confirmation. I'll try your suggestion Karl thanks a
lot. Thanks all of you for your inputs.
On Thu, Oct 4, 2012 at 5:18 PM, Constantin Makshin <cmakshin at gmail.com>wrote:
> 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>
>> 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
>> 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
>> QtConcurrent runs as many threads as there are processors.
>> Thiago Macieira - thiago.macieira (AT) intel.com
>> Software Architect - Intel Open Source Technology Center
>> Interest mailing list
>> Interest at qt-project.org
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