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Date: Sat, 06 Sep 2008 19:24:39 +0100 From: "Phil Endecott" <phil_wueww_endecott@...zphil.org> To: "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org> Subject: Re: nice and hyperthreading on atom Arjan van de Ven writes: >> Phil Endecott wrote: >> Dear Experts, >> >> I have an ASUS Eee with an Atom processor, which has hyperthreading >> enabled. If I have two processes, one nice and the other normal, they >> each get 50% of the CPU time. Of course this is what you'd expect if >> the scheduler didn't understand that the two virtual processors are not >> really independent. I'd like to fix it. > > but you cannot imfluence the cpu's scheduling of the instructions. > > As an OS one COULD decide to just not schedule the nice task at all, > but then, especially on atom where HT has a high efficiency, your cpu > is mostly idle ... Here's how I imagine it: say I have one regular task and one "nice -9" task. On a conventional uniprocessor system they would get about 90% and 10% of the CPU respectively. On the hyperthreadng system they currently get equal shares; except that the CPU is more efficient with two threads running, so you could perhaps say that they get 60% each or something like that. But 60% is still less than 90%, and I don't want my foreground interactive task being slowed down that much by this niced task. So I envisage the system spending 20% of its time running both tasks and the remaining 80% of the time running just the higher-priority task. That way, I get half of 20% = 10% spent on the nice task and half of 20% plus 80% = 90% spent on the foreground task. (Or maybe something like 12% + 92%, allowing for the hyperthreading efficiency.) Here's a link to Con Kolivas' post where he described something like this back in 2004: http://thread.gmane.org/gmane.linux.kernel/178090/focus=178882 Phil. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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