On Thu, Feb 16, 2023 at 12:50:03PM +0100, Hannes Reinecke wrote: > Hi all, > > it has come up in other threads, so it might be worthwhile to have its own > topic: > > Userspace command aborts > > As it stands we cannot abort I/O commands from userspace. > This is hitting us when running in a virtual machine: > The VM sets a timeout when submitting a command, but that > information can't be transmitted to the VM host. The VM host > then issues a different command (with another timeout), and > again that timeout can't be transmitted to the attached devices. > So when the VM detects a timeout, it will try to issue an abort, > but that goes nowhere as the VM host has no way to abort commands > from userspace. > So in the end the VM has to wait for the command to complete, causing > stalls in the VM if the host had to undergo error recovery or something. Aborts are racy. A lot of hardware implements these as a no-op, too. > With io_uring or CDL we now have some mechanism which look as if they > would allow us to implement command aborts. CDL on the other hand sounds more promising. > So this BoF will be around discussions on how aborts from userspace could be > implemented, whether any of the above methods are suitable, or whether there > are other ideas on how that could be done.
