On Wed, May 7, 2014 at 4:36 PM, Ryosuke Niwa <rn...@webkit.org> wrote:
> On Mon, May 5, 2014 at 8:02 PM, Rik Cabanier <caban...@gmail.com> wrote: > >> On Mon, May 5, 2014 at 6:23 PM, Oliver Hunt <oli...@apple.com> wrote: >> >>> On May 5, 2014, at 6:13 PM, Rik Cabanier <caban...@gmail.com> wrote: >>> >>> Do you really want a page to know that you have a fancy-pants 24-core >>>> Mac Pro rather than a little Mac mini? >>>> >>> >>> Yes! >>> If I have 24 cores ready to do work and the page can put them to use, I >>> would like it to do so. >>> At the same time, if I just have a old mac mini, I don't want the page >>> to launch 24 workers as that will exhaust my memory and cause contention. >>> >>> >>> But I don't have 24 cores available, i have 24 cores installed. You >>> have no idea what the actual workload of the system is, you don't know >>> whether any other tabs are also using workers, you only have one piece of >>> information, and that is nowhere near sufficient to make a reasonable >>> choice. >>> >> >> Sure, if I have 2 tabs and each one consumes all my CPU resources, things >> will run at half the speed and maybe even worse because of we would use >> more memory. >> > > At most at half the speed; it could be significantly worse if each worker > ended up accessing completely different parts of RAM, etc... > > Furthermore, the performance characteristics of 4 physical cores with SMT > enabled for the total of 8 logical cores is substantially different from > that of a system with 4 physical cores without SMT (4 logical) or 8 > physical cores without SMT (8 logical). In some cases, distributing work > among 8 threads concurrently in such a system (4 physical cores with SMT) > results in a much worse performance than doing so among 4 threads. > > So while I agree that providing some API to let developers know of the > number of threads that could be ran concurrently > is useful > , I'm not certain the number of installed cores is a good metrics for that. > > - R. Niwa > >
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