At 03/16/2012 04:27 PM, Jan Kiszka Wrote: > On 2012-03-16 03:38, Wen Congyang wrote: >> At 03/15/2012 06:21 PM, Wen Congyang Wrote: >>> Hi all >>> >>> When I use pci-assign, I meet the following error: >>> >>> Failed to assign irq for "hostdev0": Input/output error >>> Perhaps you are assigning a device that shares an IRQ with another device? >>> >>> Is it a bug or I miss something? >> >> Hi, Jan >> >> This problem is caused by your patch: >> commit 6919115a8715c34cd80baa08422d90496f11f5d7 >> Author: Jan Kiszka <jan.kis...@siemens.com> >> Date: Thu Mar 8 11:10:27 2012 +0100 >> >> pci_assign: Flip defaults of prefer_msi and share_intx >> >> INTx sharing is a bit more expensive than exclusive host interrupts, but >> this channel is not supposed to be used for high-performance scenarios >> anyway. Modern devices support MSI/MSI-X and do not depend on using INTx >> under critical workload, real old devices do not support INTx sharing >> anyway. >> >> For those in the middle, the user experience is much better if they just >> work even when IRQ sharing is required. If there is nothing to share, >> share_intx=off can still be applied as tuning parameter. >> >> With INTx sharing as default, the primary reason for prefer_msi=on is >> gone. Make it default off, specifically as it is known to cause troubles >> with devices that have incomplete/broken MSI support or otherwise >> stumble if host IRQ configuration does not match guest driver >> expectation. >> >> Acked-by: Alex Williamson <alex.william...@redhat.com> >> Signed-off-by: Jan Kiszka <jan.kis...@siemens.com> >> Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com> >> >> If I revert this commit. qemu can work. >> > > This should be "solvable" by passing prefer_msi=on to the pci-assign > device, or likely by updating your host kernel to latest kvm.git (to > enable INTx sharing).
Is there some way to find out if the kernel supports to enable INTx sharing? Thanks Wen Congyang > > Hmm, unfortunate. We needed a conditional default for the prefer_msi > property here. If INTx sharing doesn't work for some reason AND the user > did not ask for disabling the host-side MSI usage, we should fall back > to it again. > > Markus, is there some easy way to find out if a specific qdev property > was set due to a command line switch or was defined by the default value? > > Jan > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
