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Date: Mon, 29 Oct 2007 15:45:10 -0700 From: Jeremy Fitzhardinge <jeremy@...p.org> To: Zachary Amsden <zach@...are.com> CC: Glauber de Oliveira Costa <gcosta@...hat.com>, linux-kernel@...r.kernel.org, tglx@...utronix.de, rusty@...tcorp.com.au, --cc@...hat.com, mingo@...e.hu, avi@...amnet.com, kvm-devel@...ts.sourceforge.net, Glauber de Oliveira Costa <glauber@....localdomain>, Dan Hecht <dhecht@...are.com>, Garrett Smith <garrett@...are.com> Subject: Re: [PATCH] raise tsc clocksource rating Zachary Amsden wrote: > On Mon, 2007-10-29 at 20:10 -0300, Glauber de Oliveira Costa wrote: > >> From: Glauber de Oliveira Costa <glauber@....localdomain> >> >> tsc is very good time source (when it does not have drifts, does not >> change it's frequency, i.e. when it works), so it should have its rating >> raised to a value greater than, or equal 400. >> >> Since it's being a tendency among paravirt clocksources to use values >> around 400, we should declare tsc as even better: So we use 500. >> > > Why is the TSC better than a paravirt clocksource? In our case this is > definitely inaccurate. Paravirt clocksources should be preferred to > TSC, and both must be made available in hardware for platforms which do > not support paravirt. > > Also, please cc all the paravirt developers on things related to > paravirt, especially things with such broad effect. I think 400 is a > good value for a perfect native clocksource. >400 should be reserved > for super-real (i.e. paravirt) sources that should always be chosen over > a hardware realistic implementation in a virtual environment. > Yes, agreed. The tsc is never the right thing to use if there's a paravirt clocksource available. What's wrong with rating it 300? What inferior clocksource does it lose out to? Shouldn't that clocksource be lowered? (Why don't we just use 1 to 10?) J - 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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