Messages in this thread | | | Date | Thu, 23 Oct 2008 17:46:15 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] Skip tsc synchronization checks if CONSTANT_TSC bit is set. |
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Andi Kleen wrote: >> As far as skipping the check, it makes sense for me in the case of known >> virtualization platforms; a CPU feature bit, real or synthetic, is a >> very clean way to do that. > > I don't think adding detection for non PV Hypervisors is anywhere clean > Even if it's only VMware today, tomorrow it will be a few more > and long term you might need to support all of the obscuro hypervisors > that are out there. Just seems like a slippery slope. Either it's > paravirtual or it's not, but it should attempt to be both. If the hypervisor > doesn't emulate TSC well enough that the native code works it's entirely > reasonable to let it use some other timer, like it has been always > done in the past.
That is at least to some degree nonsense, simply because we are all well down that particular "slippery slope": we have hardware blacklists and whitelists, CPU-specific workarounds, and so on all over the place, and in that sense a hypervisor really isn't different than another hardware platform.
-hpa
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