> On 29 Sep 2016, at 14:38, Quincey Morris > <quinceymor...@rivergatesoftware.com> wrote: > > On Sep 29, 2016, at 00:15 , Gerriet M. Denkmann <g...@mdenkmann.de> wrote: >> >> dispatch_apply( nbrOfThreads, queue, ^void(size_t idx) >> >> As my computer has just 8 CPUs, I thought that using nbrOfThreads > 8 would >> be silly: adding overhead without gaining anything. >> >> Turns out this is quite wrong. One function (called threadHappyFunction) >> works more than 10 times faster using nbrOfThreads = a few ten-thousand (as >> compared to nbrOfThreads = 8). >> >> This is nice, but I would like to know why can this happen. > > What makes you think “nbrOfThreads” represents a number of threads?
Well, nothing. Just let’s call it nbrOfBlocksToBeUsedByDispatchApply, or whatever. But ultimately any of these things has to run on a CPU, of which there are no more than 8. > >> Why are the threads seemingly blocking each other? >> What is going on here? >> How can I investigate this? > > Isn’t this what Instruments is for? Might be. I already looked at Time Profiler, but failed to notice anything (maybe was looking at the wrong things) and System Trace, but did not understand what to observe or what the Instrument was telling me. Maybe some other Instrument would help? What should I look for? Kind regards, Gerriet. _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
