RW wrote: > On Wed, 22 Jul 2009 22:33:46 +0200 > Ivan Voras <ivo...@freebsd.org> wrote: > >> Scott Bennett wrote: >>> This is a curiousity question. I'm running 7.2-STABLE at >>> present on an old Inspiron XPS, which has a 3.4 GHz P4 Prescott >>> CPU. I have hyperthreading enabled in the kernel. The question >>> is: is there any appreciable performance difference to be expected >>> with this hardware setup between the ULE scheduler and the 4BSD >>> scheduler? Or does the fact that there is only one core eliminate >>> any difference in performance characteristics? >> I'd guess the second thing. It's not like there's cache to be shared >> between cores, etc. > > But with hyperthreading enabled, don't you have virtual CPUs sharing > L1 cache
Yes, > rather that cores sharing L2 cache, making the case for ULE > even stronger? If you're thinking about ULEs "soft-pinning" of processes to CPUs then I don't think so for two reasons: it's not like 4BSD forces processes ping-ponging everywhere - for 2 logical CPUs it's not that there's much choice of where to schedule a process - and thread switches between HTT logical CPUs is supposed to be cheap - I think since the L1 is shared, HTT cores have access to cached data from "the other" core for no cost.
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