On Fri, 2004-01-09 at 14:52, Stas Bekman wrote:We really need more real world benchmarks to make a good judgement. It's
probably quite certain that the performance is going to be worse if you spawn
threads, but don't deploy the benefits available exclusively to threads> (shared opcode tree, shared vars, etc). That reminds me, does anyone know what happened with the shared opcode tree? Does it not work, or is it just dwarfed by the size of the non-shared stuff? The size problems these guys are having seem to point to little or no sharing happening between threads.
I'm sure you know my PerlMonks article "Things yuu need to know before programming Perl ithreads" ( http://www.perlmonks.org/index.pl?node_id=288022 ).
I recently ran a little test that showed (at least to Devel::Size) that you have _at least_ about 250Kbyte of "data" that needs to be copied between threads if you _only_ do:
use threads; use threads::shared;
And I'm not sure whether this number isn't too low, because I don't know for sure whether the CV's in the stash haven't been counted correctly. If they were not, then you would come at about 400Kbyte of "data" for a _bare_ thread.
Loading a few modules, each with their initializations, add up _very_ quickly to several Mbytes of "data" that needs to be cloned _every_ time you start a thread. And these are _not_ simple copies: all of the stashes need to be walked to make sure that all the [SAHC]V's are properly copied to the thread's copy. So it's taking a _lot_ of CPU as well...
So yes, in general I think you can say that the data copied for each thread, quickly dwarves whatever optrees are shared.
Liz
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