On Thu, 19 May 2005 04:42, Tetsuji "Maverick" Rai wrote: > I'm wondering linux kernel's HT support is correct or not, or whether > it's a feature of P4 HT. > > I'm running boinc/seti in the background with nice=19 on my P4 2.8G HT > enabled linux box, kernel 2.6.11.9, where SMT/HT is enabled. > > I often watch system monitor applet on gnome desktop or top command in > a termianl window and see when no other applications than boinc is > running, boinc takes full power of both virtual cpus. It is designed > to run to "fill" the idle power of the cpu(s). However any > application is running, there is always some "idle" part appears on > virtual cpus, hence it looks like it wastes up to half of cpu power as > "idle." > > For ex, see this "top" result while a vmware is running. (HT is > enabled) setiathome-4.7(blah--) are the background boinc applications > with nice=19. Hyperthread sibling cpus share cpu power. If you let a nice 19 task run full power on the sibling cpu of a nice 0 task it will drain performance from the nice 0 task and make it run approximately 40% slower. The only way around this is to temporarily make the sibling run idle so that a nice 0 task gets the appropriate proportion of cpu resources compared to a nice 19 task. It is intentional and quite unique to the linux cpu scheduler as far as I can tell. On any other scheduler or OS a nice 19 "background" task will make your machine run much slower. Cheers, Con
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