On Tue, Sep 18, 2012 at 5:40 AM, Devin Heitmueller <dheitmueller@xxxxxxxxxxxxxx> wrote: Hi Devin, > This is a very common problem when attempting to use any PCI/PCIe > tuner under a hypervisor. Essentially the issue is all of the > virtualization solutions provide very poor interrupt latency, which > results in the data being lost. > > Devices delivering a high bitrate stream of data in realtime are much > more likely for this problem to be visible since such devices have > very little buffering (it's not like a hard drive controller where it > can just deliver the data slower). The problem is not specific to the > cx23885 - pretty much all of the PCI/PCIe bridges used in tuner cards > work this way, and they cannot really be blamed for expecting to run > in an environment with really crappy interrupt latency. > > I won't go as far as to say, "abandon all hope", but you're not really > likely to find any help in this forum. I can't say how happy I am that you were wrong in your guess. Quoting Konrad Rzeszutek Wilk: """ The issue as I understand is that the DVB drivers allocate their buffers from 0->4GB most (all the time?) so they never have to do bounce-buffering. While the pv-ops one ends up quite frequently doing the bounce-buffering, which implies that the DVB drivers end up allocating their buffers above the 4GB. This means we end up spending some CPU time (in the guest) copying the memory from >4GB to 0-4GB region (And vice-versa). """ You can see the original thread where this was found, together with a working patch, here: http://lists.xen.org/archives/html/xen-devel/2012-01/msg01927.html -- Javier Marcet <jmarcet@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
