On 2012-07-11 12:49, Avi Kivity wrote: > On 07/11/2012 01:18 PM, Jan Kiszka wrote: >> On 2012-07-11 11:53, Avi Kivity wrote: >>> On 07/03/2012 10:21 PM, Alex Williamson wrote: >>>> Here's the latest iteration of adding an interface to assert and >>>> de-assert level interrupts from external drivers like vfio. These >>>> apply on top of the previous argument cleanup, documentation, and >>>> sanitization patches for irqfd. It would be great to get this queued >>>> in next for linux 3.6. >>>> >>>> I believe I've addressed all the previous comments, including fixing >>>> the locking problems in eoifd. I've run this with lockdep adding >>>> and removing level irqfd/eoifd pairs without any problems. Please >>>> let me know if there are any further comments. Thanks, >>> >>> Is there any performance justification for level irqfd? Don't all >>> new/high bandwidth devices support msi, and this is just a legacy path? >> >> I think we've been there before, but the situation hasn't improved much: >> >> Apparently, some GPUs still prefer INTx over MSI. Some wireless chipsets >> too. > > I'd appreciate a couple of examples for formality's sake. >From the top of my head: NVIDIA FX3700 (granted, legacy by now), Atheros AR9287. For others, I need to check. > >> And then there is not easily replaceable legacy hardware like old >> telephony adapters or industrial I/O cards etc. that want this. > > I imagine legacy hardware will live with the speed of routing through > qemu, when running on modern platforms. Just because it's "legacy" doesn't mean it's "low performance" and "low interrupt rate". We still have classic KVM device assignment to provide fast-path INTx. But if we want to replace it midterm, I think it's necessary for VFIO to be able to provide such a path as well. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SDP-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
