Re: [PATCH v4] hw/nvme: Use ioeventfd to handle doorbell updates

[Klaus Jensen <its@irrelevant.dk>]

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On Jul 26 11:19, Klaus Jensen wrote:
> On Jul 26 15:55, Jinhao Fan wrote:
> > at 3:41 PM, Klaus Jensen <its@irrelevant.dk> wrote:
> > 
> > > On Jul 26 15:35, Jinhao Fan wrote:
> > >> at 4:55 AM, Klaus Jensen <its@irrelevant.dk> wrote:
> > >> 
> > >>> We have a regression following this patch that we need to address.
> > >>> 
> > >>> With this patch, issuing a reset on the device (`nvme reset /dev/nvme0`
> > >>> will do the trick) causes QEMU to hog my host cpu at 100%.
> > >>> 
> > >>> I'm still not sure what causes this. The trace output is a bit
> > >>> inconclusive still.
> > >>> 
> > >>> I'll keep looking into it.
> > >> 
> > >> I cannot reproduce this bug. I just start the VM and used `nvme reset
> > >> /dev/nvme0`. Did you do anything before the reset?
> > > 
> > > Interesting and thanks for checking! Looks like a kernel issue then!
> > > 
> > > I remember that I'm using a dev branch (nvme-v5.20) of the kernel and
> > > reverting to a stock OS kernel did not produce the bug.
> > 
> > I’m using 5.19-rc4 which I pulled from linux-next on Jul 1. It works ok on
> > my machine.
> 
> Interesting. I can reproduce on 5.19-rc4 from torvalds tree. Can you
> drop your qemu command line here?
> 
> This is mine.
> 
> /home/kbj/work/src/qemu/build/x86_64-softmmu/qemu-system-x86_64 \
>   -nodefaults \
>   -display "none" \
>   -machine "q35,accel=kvm,kernel-irqchip=split" \
>   -cpu "host" \
>   -smp "4" \
>   -m "8G" \
>   -device "intel-iommu" \
>   -netdev "user,id=net0,hostfwd=tcp::2222-:22" \
>   -device "virtio-net-pci,netdev=net0" \
>   -device "virtio-rng-pci" \
>   -drive "id=boot,file=/home/kbj/work/vol/machines/img/nvme.qcow2,format=qcow2,if=virtio,discard=unmap,media=disk,read-only=no" \
>   -device "pcie-root-port,id=pcie_root_port1,chassis=1,slot=0" \
>   -device "nvme,id=nvme0,serial=deadbeef,bus=pcie_root_port1,mdts=7" \
>   -drive "id=null,if=none,file=null-co://,file.read-zeroes=on,format=raw" \
>   -device "nvme-ns,id=nvm-1,drive=nvm-1,bus=nvme0,nsid=1,drive=null,logical_block_size=4096,physical_block_size=4096" \
>   -pidfile "/home/kbj/work/vol/machines/run/null/pidfile" \
>   -kernel "/home/kbj/work/src/kernel/linux/arch/x86_64/boot/bzImage" \
>   -append "root=/dev/vda1 console=ttyS0,115200 audit=0 intel_iommu=on" \
>   -virtfs "local,path=/home/kbj/work/src/kernel/linux,security_model=none,readonly=on,mount_tag=kernel_dir" \
>   -serial "mon:stdio" \
>   -d "guest_errors" \
>   -D "/home/kbj/work/vol/machines/log/null/qemu.log" \
>   -trace "pci_nvme*"

Alright. It was *some* config issue with my kernel. Reverted to a
defconfig + requirements and the issue went away.

I'll try to track down what happended, but doesnt look like qemu is at
fault here.

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