I was going to ask about DMA but wasn't sure, what does the host report on DMA and what does the guest OS report from cat /proc/dma?
Just curious if the host OS gives bogo-dma. I am looking at timing issues which a think Free Switch has figured out along with T38 a while ago. I care slightly about using an actual TDM card since that can be handled by Redfone or a USB device. Thanks, Steve Totaro On Sun, Jul 10, 2011 at 4:11 AM, Tzafrir Cohen <[email protected]>wrote: > On Fri, Jul 08, 2011 at 07:28:39PM -0400, Doug Lytle wrote: > > Can you say a Virtualized Asterisk with a PRI card! > > > > http://www.phoronix.com/scan.php?page=news_item&px=OTY0OQ > > I'm not sure this is relevant to your everyday PRI card. > > Simple pass-through of PCI is rather simple to implement. It has been > implemented for quite some time in e.g. qemu, IIRC. > > But there's one important feature that is tricky to implement: DMA. > DMA allows a PCI card to basically free access to the memory of the > system, without the CPU getting in the middle. Emulating this with the > host CPU in the middle will work, but is exepnsive. But the host does > not want to give the guest free access to the host's memory. > > The solution: IOMMU: http://en.wikipedia.org/wiki/Iommu . > The CPU of the system has a Memory Management Unit (MMU) that > maps virtual address spaces to processes. Likewise we know prevent the > IO card from seeing physical addresses. Rather, it sees virtual > addresses mapped by the IOMMU. Just like the operating system maps > addresses for processes, the hypervisor maps address ranger to IO cards. > > See also the link in that Phoronix article: > http://www.ibm.com/developerworks/linux/library/l-pci-passthrough/ > > I'm not well familiar with the relevant hardware, but I believe that not > only not every CPU supports this, but many (most?) PCI cards don't > support IOMMU. > > -- > Tzafrir Cohen > icq#16849755 jabber:[email protected] > +972-50-7952406 mailto:[email protected] > http://www.xorcom.com iax:[email protected]/tzafrir > > -- > _____________________________________________________________________ > -- Bandwidth and Colocation Provided by http://www.api-digital.com -- > New to Asterisk? Join us for a live introductory webinar every Thurs: > http://www.asterisk.org/hello > > asterisk-users mailing list > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users >
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