From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: Xen 4.2.0-rc4 issues with DVB tuner Date: Tue, 18 Sep 2012 15:34:02 -0400 Message-ID: <20120918193401.GA7667@phenom.dumpdata.com> References: <20120917142851.GB14012@phenom.dumpdata.com> <20120918171725.GA14462@phenom.dumpdata.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Javier Marcet Cc: Xen Devel Mailing list List-Id: xen-devel@lists.xenproject.org On Tue, Sep 18, 2012 at 08:26:33PM +0200, Javier Marcet wrote: > On Tue, Sep 18, 2012 at 7:17 PM, Konrad Rzeszutek Wilk > wrote: > = > >> I have some news from the linux-media mailing list. There, Devin Heitm= ueller, > >> said this: > >> > >> """ > >> > Initially I thought Xen would be the cause of the problem, but after > >> > having written on > >> > the Xen development mailing list and talked about it with a couple > >> > developers, it isn't > >> > very clear where the problem is. So far I haven't been able to get t= he > >> > smallest warning > >> > or error. > >> > >> 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. > >> """ > > > > Not sure about the interrupt latency. If you run this little program > > http://darnok.org/xen/read_interrupts.c > > when capturing in both dom0 and in baremetal are the rate about the > > same? > >> > >> What I don=B4t understand is how graphics pass through even works > >> and a tuner card has problems due to the introduced latencies in the > >> IRQs. > > > > The latency is very very miniscule. One could actually verify that this > > is a problem by inserting said latency in the driver so that under > > baremetal the latency would show up. > > > > But the other issue is that if the data is being lost you would at least > > get some. So the buffers ought to have "something" in them? Maybe that > > depends on what compression you use on the coder? If you jus do YUV420 > > or the RGB variants and just do a simple 'cat /dev/vide0 > /tmp/file' > > does the output contain anything? Or is just a blob of empty data? > = > The output contains data, part of the mpeg stream without any continuity. > = I see. > >> Do you have any more info about this? > > > > The other issue could be related to the vmalloc_32 being in usage > > and not using the DMA API. > > > > I recall posting a patch for this .. Ah: > > http://lists.xen.org/archives/html/xen-devel/2012-01/msg01927.html > > > > Perhaps this is the issue? > = > Bingo Konrad! That was it :) At least I have just applied the patch, > rebooted under Xen and this time I got a good dump. Woohoo! > = > Right now I have my usual system running flawlessly under Xen. Time to > take a look again at the suspend/resume issue which I nearly had > working a few days ago. Keep in mind that for the suspend/resume you need out of mainline patches for right now. I hadn't yet upstreamed all the parts. They are in git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git devel/acpi-s3.vXX (I believe 11 would apply cleanly to your tree?) Keep in mind that there were some bugs in Xen 4.2 in regards to resume. Look on xen-devel for emails between Jan and Ben Guthro. > = > Thanks a lot for all your help :) > = > P.S. I'm going to post this info on the linux media mailing list. If you could CC me on it I can provide the technical explanation for the 'DMA-API-ing the vmalloc_32' call.