Messages in this thread | | | Date | Fri, 11 Nov 2011 16:51:00 -0800 | From | Chris Wright <> | Subject | Re: [PATCH] intel-iommu: Default to non-coherent for domains unattached to iommus |
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* Roland Dreier (roland@purestorage.com) wrote: > On Fri, Nov 11, 2011 at 4:37 PM, David Woodhouse <dwmw2@infradead.org> wrote: > > This brain-damage only affects the first chipsets > > from before we worked out that cache incoherency was a *really* f*cking > > stupid idea, doesn't it? > > As we talked about at KS, I have some Westmere EP (ie latest > and greatest server platform) systems where the BIOS exposes > an option that allows choosing VT-d coherency on or off, and > defaults it to "off".
That's just more brain damage AFAICT. Esp. if you do performance testing (and choose not to use passthrough mode)... have and it's quite measurable. I switched default to on long time ago, w/out issue.
> What is the "official" Intel line on coherency with Westmere and > Tylersburg -- because as I also mentioned, I was seeing some > problems with VT-d and the default "coherency off" setting that > looked like the IOMMU HW is getting stale PTEs (ie a missing > or not working cache flush).
That sounds like sw bugs more than official recommendation issue.
thanks, -chris
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