On Tue, 2010-01-26 at 21:46 -0500, Peter Budny wrote: > Andy Walls <[email protected]> writes: > > > On Mon, 2010-01-25 at 21:51 -0500, Andy Walls wrote: > > > >> You are certainly welcome to look at the driver for bugs. If trying to > >> grok what the driver is doing WRT to data transfers from hardware, I > >> would suggest looking at these: > > > > > >> linux/drivers/media/video/ivtv/ivtv-irq.c:ivtv_irq_enc_dma_complete() > > > > Hmm. If the kernel's software IOMMU implementation is active on your > > machine, ivtv-irq.c:dma_post() can end up performing a buffer memcpy() > > in an interrupt context for buffers when calling > > ivtv_buf_sync_for_cpu(). > > > > I need to fix that. The ivtv driver should try to avoid buffer > > memcpy()'s in an interrupt context for system performance reasons. > > > > > > Can you check your dmesg or messages log for this: > > > > "PCI-DMA: Using software bounce buffering for IO (SWIOTLB)" > > I don't see this in the log. Would I have to enable anything special to > get it, such as IOMMU debugging?
No. It's logged at the kern.info level which means it should show up in dmesg if it were enabled. So back to more thought experiments and staring at code for the moment. I may try looking at what ftrace can tell me about ivtv driver latencies: http://lwn.net/Articles/322666/ http://lwn.net/Articles/322731/ http://lwn.net/Articles/366796/ http://lwn.net/Articles/365835/ But I'll need to find free time to play with FTrace before I can suggest specific commands. Regards, Andy _______________________________________________ ivtv-users mailing list [email protected] http://ivtvdriver.org/mailman/listinfo/ivtv-users
