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Message-ID: <87ws0owd8q.fsf@basil.nowhere.org> Date: Tue, 15 Dec 2009 14:58:13 +0100 From: Andi Kleen <andi@...stfloor.org> To: Zachary Amsden <zamsden@...hat.com> Cc: kvm@...r.kernel.org, Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>, Joerg Roedel <joerg.roedel@....com>, linux-kernel@...r.kernel.org, Dor Laor <dlaor@...hat.com> Subject: Re: [PATCH RFC: kvm tsc virtualization 15/20] Fix longstanding races Zachary Amsden <zamsden@...hat.com> writes: > > Damn, this is complicated crap. The analagous task in real life would > be keeping a band of howler monkeys, each in their own tree, singing in > unison while the lead vocalist jumps from tree to tree, and meanwhile, > an unseen conductor keeps changing the tempo the piece is played at. > Thankfully, there are no key changes, however, occasionally new trees > sprout up at random and live ones fall over. On CPUs where the TSC frequency is not constant typically you can't tell exactly when the frequency changes. So you would always have a race window where the frequency is unknown and wrong results occur. This can be worked around, but it's quite complicated. The safe way is to not use the TSC on such CPUs. -Andi -- ak@...ux.intel.com -- Speaking for myself only. -- 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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