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Date: Sun, 07 Sep 2008 11:34:58 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Ulrich Drepper <drepper@...il.com> Cc: Arjan van de Ven <arjan@...radead.org>, Phil Endecott <phil_wueww_endecott@...zphil.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: nice and hyperthreading on atom On Sat, 2008-09-06 at 11:30 -0700, Ulrich Drepper wrote: > On Sat, Sep 6, 2008 at 9:42 AM, Arjan van de Ven <arjan@...radead.org> wrote: > > 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 ... > > One thread being idle is even on Atom the right thing to do in some > situations. If you have processes which, when HT is used, experience > high pressure on the common cache(s) then you should not schedule them > together. We can theoretically find out whether this is the case > using the PMCs. With perfmon2 hopefully on the horizon soon it might > actually be possible to automatically make these measurements. > > There is another aspect I talked to Peter about already. We really > want concurrent threat scheduling in some cases. For the > implementation of helper threads you don't want two threads to be > scheduled independently, you want them to be scheduled on a HT pair. > Currently this isn't possible except by pinning them to fixed threads. > We really want to have a new way to express this type of scheduling > (Peter, how did you call it?) Really helps if you make sure I'm on the CC ;-) I think I called it something like affinity grouping - but I'm still a bit scared of the bin-packing issues involved - those will really mess up the already complex balancing rules. -- 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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