[Bug 199727] CPU freezes in KVM guests during high IO load on host

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=199727

--- Comment #14 from Stefan Hajnoczi (stefanha@gmail.com) ---
(In reply to Roland Kletzing from comment #13)
> hello, thanks - aio=io_uring is no better, the only real way to get to a
> stable system is virtio-scsi-single/iothreads=1/aio=threads
> 
> the question is why aio=native and io_uring has issues and threads has not...

Are you using cache=none with io_uring and the io_uring_enter(2) syscall is
blocking for a long period of time?

aio=threads avoids softlockups because the preadv(2)/pwritev(2)/fdatasync(2)
syscalls run in worker threads that don't take the QEMU global mutex. Therefore
vcpu threads can execute even when I/O is stuck in the kernel due to a lock.

io_uring should avoid that problem too because it is supposed to submit I/O
truly asynchronously.

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